Hormonal Communication

Hormones are important messages both within the brain and between the brain and the body.

In addition to the nervous system, the endocrine system is a major communication system of the body. While the nervous system uses neurotransmitters as its chemical signals, the endocrine system uses hormones. The pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid, thymus, and even fat are all sources of hormones. The endocrine system works in large part by acting on neurons in the brain, which controls the pituitary gland. The pituitary gland secretes factors into the blood that act on the endocrine glands to either increase or decrease hormone production. This is referred to as a feedback loop, and it involves communication from the brain to the pituitary to an endocrine gland and back to the brain. This system is very important for the activation and control of basic behavioral activities, such as sex; emotion; responses to stress; and eating, drinking, and the regulation of body functions, including growth, reproduction, energy use, and metabolism. The way the brain responds to hormones indicates that the brain is very malleable and capable of responding to environmental signals.

The brain contains receptors for thyroid hormones (those produced by the thyroid) and the six classes of steroid hormones, which are synthesized from cholesterol — androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and vitamin D. The receptors are found in selected populations of neurons in the brain and relevant organs in the body. Thyroid and steroid hormones bind to receptor proteins that in turn bind to DNA and regulate the action of genes. This can result in long-lasting changes in cellular structure and function.

The brain has receptors for many hormones; for example, the metabolic hormones insulin, insulin-like growth factor, ghrelin, and leptin. These hormones are taken up from the blood and act to affect neuronal activity and certain aspects of neuronal structure.

In response to stress and changes in our biological clocks, such as day and night cycles and jet lag, hormones enter the blood and travel to the brain and other organs. In the brain, hormones alter the production of gene products that participate in synaptic neurotransmission as well as affect the structure of brain cells. As a result, the circuitry of the brain and its capacity for neurotransmission are changed over a course of hours to days. In this way, the brain adjusts its performance and control of behavior in response to a changing environment.

Hormones are important agents of protection and adaptation, but stress and stress hormones, such as the glucocorticoid cortisol, can also alter brain function, including the brain’s capacity to learn. Severe and prolonged stress can impair the ability of the brain to function normally for a period of time, but the brain is also capable of remarkable recovery.

Reproduction in females is a good example of a regular, cyclic process driven by circulating hormones and involving a feedback loop: The neurons in the hypothalamus produce gonadotropin-releasing hormone (GnRH), a peptide that acts on cells in the pituitary. In both males and females, this causes two hormones — the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) — to be released into the bloodstream. In females, these hormones act on the ovary to stimulate ovulation and promote release of the ovarian hormones estradiol and progesterone. In males, these hormones are carried to receptors on cells in the testes, where they promote spermatogenesis and release the male hormone testosterone, an androgen, into the bloodstream. Testosterone, estrogen, and progesterone are often referred to as sex hormones.

In turn, the increased levels of testosterone in males and estrogen in females act on the hypothalamus and pituitary to decrease the release of FSH and LH. The increased levels of sex hormones also induce changes in cell structure and chemistry, leading to an increased capacity to engage in sexual behavior. Sex hormones also exert widespread effects on many other functions of the brain, such as attention, motor control, pain, mood, and memory.

Sexual differentiation of the brain is caused by sex hormones acting in fetal and early postnatal life, although recent evidence suggests genes on either the X or Y chromosome may also contribute to this process. Scientists have found statistically and biologically significant differences between the brains of men and women that are similar to sex differences found in experimental animals. These include differences in the size and shape of brain structures in the hypothalamus and the arrangement of neurons in the cortex and hippocampus. Sex differences go well beyond sexual behavior and reproduction and affect many brain regions and functions, ranging from mechanisms for perceiving pain and dealing with stress to strategies for solving cognitive problems. That said, however, the brains of men and women are more similar than they are different.

Anatomical differences have also been reported between the brains of heterosexual and homosexual men. Research suggests that hormones and genes act early in life to shape the brain in terms of sex-related differences in structure and function, but scientists are still putting together all the pieces of this puzzle.

How LASIK Surgery is done

LASIK, or "laser-assisted in situ keratomileusis," is the most commonly performed laser eye surgery to treat myopia (nearsightedness), hyperopia(farsightedness) and astigmatism.

Like other types of refractive surgery, the LASIK procedure reshapes the cornea to enable light entering the eye to be properly focused onto the retina for clearer vision.
In most cases, laser eye surgery is pain-free and completed within 15 minutes for both eyes. The results — improved vision without eyeglasses or contact lenses — can usually be seen in as little as 24 hours.
If you're not a good LASIK candidate, a number of other vision correction surgeries are available, such as PRK and LASEK laser eye surgery and phakic IOL surgery. Your eye doctor will determine if one of these procedures is suitable for your condition and, if so, which technique is best.

Want a visual? View our LASIK slide show!

How Is LASIK Surgery Performed?

First, your eye surgeon uses either a mechanical surgical tool called a microkeratome or a femtosecond laser to create a thin, circular "flap" in the cornea.
The surgeon then folds back the hinged flap to access the underlying cornea (called the stroma) and removes some corneal tissue using an excimer laser.
This highly specialized laser uses a cool ultraviolet light beam to remove ("ablate") microscopic amounts of tissue from the cornea to reshape it so it more accurately focuses light on the retina for improved vision.
For nearsighted people, the goal is to flatten the cornea; with farsighted people, a steeper cornea is desired.

Excimer lasers also can correct astigmatism by smoothing an irregular cornea into a more normal shape. It is a misconception that LASIK cannot treat astigmatism.

How Lungs Work

Why are the lungs important?
Oxygen, a basic gas, is needed by every cell in your body in order to live. The air that comes into the body through the lungs contains oxygen and other gases. In the lungs, the oxygen is moved into the bloodstream and carried through the body. At each cell in the body, the oxygen cells are exchanged for waste gas called carbon dioxide. The bloodstream then carries this waste gas back to the lungs where the waste gas is removed from the blood stream and then exhaled from the body. This vital process, called gas exchange, is performed automatically by the lungs and respiratory system.

In addition to gas exchange, the respiratory system performs other roles important to breathing. These include:

• Bringing air to the proper body temperature.
• Moisturizing the inhaled air to the right humidity.
• Protecting the body from harmful substances. This is done by coughing, sneezing, filtering, or swallowing them.
• The sense of smell.

The Parts of the Respiratory System and How They Work

AIRWAYS
The SINUSES are hollow spaces in the bones of the head. Small openings connect them to the nose. The functions they serve include helping to regulate the temperature and humidity of air breathed in.

The NOSE is the preferred entrance for outside air into the respiratory system. The hairs that line the wall are part of the air-cleaning system.

Air also enters through the MOUTH, especially in people who have a mouth-breathing habit or whose nasal passages may be temporarily obstructed, as by a cold or during heavy exercise.

The THROAT collects incoming air from the nose and mouth and passes it downward to the windpipe (trachea).

The WINDPIPE (trachea) is the passage leading from the throat to the lungs.

The windpipe divides into the two main BRONCHIAL TUBES, one for each lung, which subdivide into each lobe of the lungs. These, in turn, subdivide further.

Lungs and Blood Vessels
The right lung is divided into three LOBES, or sections. Each lobe is like a balloon filled with sponge-like tissue. Air moves in and out through one opening -- a branch of the bronchial tube.

The left lung is divided into two LOBES.

The PLEURA are the two membranes, actually one continuous one folded on itself, that surround each lobe of the lungs and separate the lungs from the chest wall.

The bronchial tubes are lined with CILIA (like very small hairs) that have a wave-like motion. This motion carries MUCUS (sticky phlegm or liquid) upward and out into the throat, where it is either coughed up or swallowed. The mucus catches and holds much of the dust, germs, and other unwanted matter that has invaded the lungs. You get rid of this matter when you cough, sneeze, clear your throat or swallow.

The smallest subdivisions of the bronchial tubes are called BRONCHIOLES, at the end of which are the air sacs or alveoli.

The ALVEOLI are the very small air sacs that are the destination of air breathed in.

The CAPILLARIES are blood vessels that are imbedded in the walls of the alveoli. Blood passes through the capillaries, brought to them by the PULMONARY ARTERY and taken away by the PULMONARY VEIN. While in the capillaries the blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from the air in the alveoli.

Muscles and Bones
The DIAPHRAGM is the strong wall of muscle that separates the chest cavity from the abdominal cavity. By moving downward, it creates suction in the chest to draw in air and expand the lungs.

The RIBS are bones supporting and protecting the chest cavity. They move to a limited degree, helping the lungs to expand and contract.

Keeping Lungs Healthy

Taking good care of yourself every day will help keep your lungs healthy. Good health habits like eating a balanced diet, exercising and reducing the stress in your life will help you breathe easier.

How Nucleotides are added in DNA Replication

DNA replication is the process of producing two identical replicas from one original DNA molecule. This biological process occurs in all living organisms and is the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as template for the production of the complementary strand, a process referred to as semiconservative replication. Cellular proofreading and error-checking mechanisms ensure near perfect fidelity for DNA replication.

In a cell, DNA replication begins at specific locations, or origins of replication, in the genome.Unwinding of DNA at the origin and synthesis of new strands results in replication forks growing bidirectional from the origin. A number of proteins are associated with the replication fork which helps in terms of the initiation and continuation of DNA synthesis. Most prominently, DNA polymerase synthesizes the new DNA by adding complementary nucleotides to the template strand.

DNA replication can also be performed in vitro (artificially, outside a cell). DNA polymerases isolated from cells and artificial DNA primers can be used to initiate DNA synthesis at known sequences in a template DNA molecule. The polymerase chain reaction (PCR), a common laboratory technique, cyclically applies such artificial synthesis to amplify a specific target DNA fragment from a pool of DNA.

How the Krebs Cycle Works

The citric acid cycle – also known as the tricarboxylic acid cycle (TCA cycle), or the Krebs cycle, – is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP). In addition, the cycle provides precursors of certain amino acids as well as the reducing agent NADH that is used in numerous other biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.
The name of this metabolic pathway is derived from citric acid (a type of tricarboxylic acid) that is consumed and then regenerated by this sequence of reactions to complete the cycle. In addition, the cycle consumes acetate (in the form of acetyl-CoA) and water, reduces NAD+ to NADH, and produces carbon dioxide as a waste byproduct. The NADH generated by the TCA cycle is fed into the oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of ATP.

In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. In prokaryotic cells, such as bacteria which lack mitochondria, the TCA reaction sequence is performed in the cytosol with the proton gradient for ATP production being across the cell's surface (plasma membrane) rather than the inner membrane of the mitochondrion.

Hydrochloric Acid Production of the Stomach

Gastric acid is a digestive fluid, formed in the stomach. It is composed of hydrochloric acid (HCl) (around 0.5%, or 5000 parts per million) as high as 0.1 M,[1] potassium chloride (KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of amino acids. Gastric acid is produced by cells lining the stomach, which are coupled in feedback systems to increase acid production when needed. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring that it does not become too acidic. These cells also produce mucus, which forms a viscous physical barrier to prevent gastric acid from damaging the stomach. Cells in the beginning of the small intestine, or duodenum, further produce large amounts of bicarbonate to completely neutralize any gastric acid that passes further down into the digestive tract.

Gastric acid is produced by parietal cells (also called oxyntic cells) in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the gastric acid is secreted into the lumen of the stomach. These cells are part of epithelial fundic glands in the gastric mucosa. The pH of gastric acid is 1.5 to 3.5 [2] in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as alkaline tide.

The resulting highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection.

Integration and Excision of a Plasmid

Multicopy plasmids have greatly facilitated gene structure-function studies. However, the use of such plasmids can lead to high-copy-number artifacts, especially in physiological studies. Thus, several methods have been developed for recombining genes on bacterial chromosomes in order to study their functions in single copies. Such methods are frequently used to construct novel Escherichia coli strains that stably express foreign genes for use in both basic research and biotechnology (5, 18, 27). However, the development of strains encoding complex metabolic or regulatory pathways poses special problems that often require manipulating many genes and expressing them individually at different levels or under separate regulatory controls. To address these concerns, we have developed a series of plasmid-host systems for the introduction of multiple genes into the same cell in single copies. Our approach is based on genome targeting systems that utilize plasmids carrying a conditional-replication origin and a phage attachment (attP) site (17). We refer to our plasmids as CRIM (conditional-replication, integration, and modular) plasmids. CRIM plasmids can be integrated into or retrieved from their bacterial attachment (attB) site by supplying phage integrase (Int) without or with excisionase (Xis) in trans.

Advantages of our CRIM plasmid-host systems include the use of alternative attP andattB sites (for phages λ, HK022, 80, P21, and P22) and different selectable markers (for chloramphenicol, gentamicin, kanamycin, spectinomycin and streptomycin, tetracycline, and trimethoprim resistance) in conjunction with a polylinker or promoter (ParaB, PrhaB,PrhaS, Ptac, Psyn1, and Psyn4) for ectopic expression of the cloned gene(s). These CRIM plasmids have the γ replication origin of R6K, which requires the trans-acting Π protein (encoded by pir) for replication. So, they replicate at a medium (15 per cell) or high (250 per cell) plasmid copy number in pir+ or pir-116 (high-copy-number mutant) E. coli hosts (28), respectively. Int helper plasmids are used for integration of CRIM plasmids into the corresponding chromosomal attB sites of normal (non-pir) hosts, which are nonpermissive for CRIM plasmid replication. Xis/Int helper plasmids are used for excision (“curing”) of the respective CRIM plasmids from the chromosome, e.g., to verify that phenotypes are due to their presence. Xis/Int helper plasmids are also used for retrieval (cloning) of CRIM plasmids from the chromosome, e.g., to recover a particular CRIM plasmid after screening of CRIM plasmid or mutant libraries.

Since integration and retrieval involve phage-site-specific recombination events, the original and recovered plasmids are identical. CRIM plasmids can therefore be used for the construction of gene (or mutant) libraries that can be directly integrated into bacterial chromosomes in single copies for screening or selection purposes. Afterwards, CRIM plasmids can be retrieved from individual cells or en masse. The recovered plasmids can then be propagated as plasmids for molecular analysis or integrated directly into the chromosomes of other hosts for subsequent processing without further in vitro manipulation steps. We previously found similar oriRγ attλ plasmids to be extremely useful in mutagenesis studies, especially when it was important that the mutated gene be free of plasmid copy number effects (16). We also found them to be useful in studying genes from diverse bacteria, including gram-negative and -positive cells (14, 15, 25, 34). Our versatile CRIM plasmid-host systems should be widely useful in gene structure-function studies. Here we describe our basic set of CRIM plasmids, the requisite helper plasmids, and how to use them.

Ionic vs Covalent Bonding

Covalent Bonds vs Ionic Bonds

There are two types of atomic bonds - ionic bonds and covalent bonds. They differ in their structure and properties. Covalent bondsconsist of pairs of electrons shared by two atoms, and bind the atoms in a fixed orientation. Relatively high energies are required to break them (50 - 200 kcal/mol). Whether two atoms can form a covalent bond depends upon their electronegativity i.e. the power of an atom in a molecule to attract electrons to itself. If two atoms differ considerably in their electronegativity - as sodium and chloride do - then one of the atoms will lose its electron to the other atom. This results in a positively charged ion (cation) and negatively charged ion (anion). The bond between these two ions is called an ionic bond.

	Covalent Bonds	Ionic Bonds
State at room temperature:	Liquid or gaseous	Solid
Polarity:	Low	High
Formation:	A covalent bond is formed between two non-metals that have similar electronegativities. Neither atom is "strong" enough to attract electrons from the other. For stabilization, they share their electrons from outer molecular orbit with others	An ionic bond is formed between a metal and a non-metal. Non-metals(-ve ion) are "stronger" than the metal(+ve ion) and can get electrons very easily from the metal. These two opposite ions attract each other and form the ionic bond.
Shape:	Definite shape	No definite shape
Melting point:	low	High
What is it?:	Covalent bonding is a form of chemical bonding between two non metallic atoms which is characterized by thesharing of pairs of electrons between atoms and other covalent bonds.	Ionic bond, also known as electrovalent bond, is a type of bond formed from the electrostatic attraction between oppositely charged ions in a chemical compound. These kinds of bonds occur mainly between a metallic and a non metallic atom.
Boiling point:	Low	High
Examples:	Methane (CH4), Hydro Chloric acid (HCl)	Sodium chloride (NaCl), Sulphuric Acid (H2SO4 )
Occurs between:	Two non-metals

Kidney Function Counter current Mechanism

A countercurrent multiplier system is a mechanism that expends energy to create a concentration gradient.

It is found widely in nature and especially in mammalian organs. For example, it can refer to the process that is underlying the process of urine concentration, that is, the production of hyperosmotic urine by the mammalian kidney. The ability to concentrate urine is also present in birds.[

Countercurrent multiplication is frequently mistaken for countercurrent exchange, a similar but different mechanism where gradients are maintained, but not established.

Physiological principles
The term derives from the form and function of the loop of Henle, which consists of two parallel limbs of renal tubules running in opposite directions, separated by the interstital space of the renal medulla.

The descending limb of the loop of Henle is permeable to water but impermeable to solutes, due to the presence of aquaporin 1 in its tubular wall. Thus water moves across the tubular wall into the medullary space, making the filtrate hypertonic.
The ascending limb is impermeable to water (because of a lack of aquaporin, a common transporter protein for water channels in all cells except the walls of the ascending limb of the loop of Henle) but permeable to solutes, but here Na+, Cl−, and K+ are actively transported into the medullary space, making the filtrate hypotonic (with a higher water potential). This constitutes the single effect of the countercurrent multiplication process.
Active transport of these ions from the thick ascending limb creates an osmotic pressure drawing water from the descending limb into the hyperosmolar medullary space, making the filtrate hypertonic (with a lower water potential).
The countercurrent flow within the descending and ascending limb thus increases, or multiplies the osmotic gradient between tubular fluid and interstitial space.

Details
Countercurrent multiplication was originally studied as a mechanism whereby urine is concentrated in the nephron. Initially studied in the 1950s by Gottschalk and Mylle following Werner Kuhn's postulations,this mechanism gained popularity only after a series of complicated micropuncture experiments.

The proposed mechanism consists of pump, equilibration, and shift steps. In the proximal tubule, the osmolarity is isomolar to plasma (300 mOsm/L). In a hypothetical model where there was no equilibration or pump steps, the tubular fluid and interstitial osmolarity would be 300 mOsm/L as well.{Respicius Rwehumbiza, 2010}

Pump: The Na+/K+/2Cl− transporter in the ascending limb of the loop of Henle helps to create a gradient by shifting Na+ into the medullary interstitium. The thick ascending limb of the loop of Henle is the only part of the nephron lacking in aquaporin—a common transporter protein for water channels. This makes the thick ascending limb impermeable to water. The action of the Na+/K+/2Cl− transporter therefore creates a hypoosmolar solution in the tubular fluid and a hyperosmolar fluid in the interstitium, since water cannot follow the solutes to produce osmotic equilibrium.

Equilibration: Since the descending limb of the loop of henle consists of very leaky epithelium, the fluid inside the descending limb becomes hyperosmolar.

Shift: The movement of fluid through the tubules causes the hyperosmotic fluid to move further down the loop. Repeating many cycles causes fluid to be near isosmolar at the top of Henle's loop and very concentrated at the bottom of the loop. Interestingly, animals with a need for very concentrated urine (such as desert animals) have very long loops of Henle to create a very large osmotic gradient. Animals that have abundant water on the other hand (such as beavers) have very short loops. The vasa recta have a similar loop shape so that the gradient does not dissipate into the plasma.

The mechanism of counter current multiplication works together with the vasa recta's counter current exchange to prevent the wash out of salts and maintain a high osmolarity at the inner medulla

Kidney Function II

The kidneys are bean-shaped organs that serve several essential regulatory roles in vertebrate animals. They remove excess organic molecules (e.g., glucose) from the blood, and it is by this action that their best-known function is performed: the removal of waste products of metabolism (e.g., urea, though 90% of this is reabsorbed along the nephron.) They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure (via maintaining salt and water balance). They serve the body as a natural filter of the blood, and remove water soluble wastes, which are diverted to the urinary bladder. In producing urine, the kidneys excrete wastes such as urea and ammonium, and they are also responsible for the reabsorption of water, glucose, and amino acids. The kidneys also produce hormones including calcitriol, erythropoietin, and the enzyme renin, the last of which indirectly acts on the kidney in negative feedback.

Located at the rear of the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary bladder.

Renal physiology is the study of kidney function, while nephrology is the medical specialty concerned with kidney diseases. Diseases of the kidney are diverse, but individuals with kidney disease frequently display characteristic clinical features. Common clinical conditions involving the kidney include the nephritic and nephrotic syndromes, renal cysts, acute kidney injury, chronic kidney disease, urinary tract infection, nephrolithiasis, and urinary tract obstruction. Various cancers of the kidney exist; the most common adult renal cancer is renal cell carcinoma. Cancers, cysts, and some other renal conditions can be managed with removal of the kidney, or nephrectomy. When renal function, measured by glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not normally harmful, kidney stones can be painful, and repeated, chronic formation of stones can scar the kidneys. The removal of kidney stones involves ultrasound treatment to break up the stones into smaller pieces, which are then passed through the urinary tract. One common symptom of kidney stones is a sharp to disabling pain in the medial/lateral segments of the lower back or groin.

Lymphatic System

The lymphatic system is part of the circulatory system, comprising a network of lymphatic vessels that carry a clear fluid called lymph (from Latin lympha meaning water) directionally towards the heart. The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Unlike the cardiovascular system the lymphatic system is not a closed system. The human circulatory system processes an average of 20 litres of blood per day through capillary filtration which removes plasma while leaving the blood cells. Roughly 17 litres of the filtered plasma get reabsorbed directly into the blood vessels, while the remaining 3 litres are left behind in the interstitial fluid. One of the main functions of the lymph system is to provide an accessory route for these excess 3 litres per day to get returned to the blood.

The other main function is that of defense in the immune system. Lymph is very similar to blood plasma but contains lymphocytes and other white blood cells. It also contains waste products and debris of cells together with bacteria and protein. Associated organs composed of lymphoid tissue are the sites of lymphocyte production. Lymphocytes are concentrated in the lymph nodes. The spleen and the thymus are also lymphoid organs of the immune system. The tonsils are lymphoid organs that are also associated with the digestive system. Lymphoid tissues contain lymphocytes, and also contain other types of cells for support. The system also includes all the structures dedicated to the circulation and production of lymphocytes (the primary cellular component of lymph), which also includes the bone marrow, and the lymphoid tissue associated with the digestive system.

The blood does not come into direct contact with the parenchymal cells and tissues in the body, but constituents of the blood first exit the microvascular exchange blood vessels to become interstitial fluid, which comes into contact with the parenchymal cells of the body. Lymph is the fluid that is formed when interstitial fluid enters the initial lymphatic vessels of the lymphatic system. The lymph is then moved along the lymphatic vessel network by either intrinsic contractions of the lymphatic passages or by extrinsic compression of the lymphatic vessels via external tissue forces (e.g. the contractions of skeletal muscles), or by lymph hearts in some animals. The organization of lymph nodes and drainage follows the organization of the body into external and internal regions; therefore, the lymphatic drainage of the head, limbs, and body cavity walls follows an external route, and the lymphatic drainage of the thorax, abdomen, and pelvic cavities follows an internal route.Eventually, the lymph vessels empty into the lymphatic ducts, which drain into one of the two subclavian veins, near their junction with the internal jugular veins.

Maturation of the Follicle

In biology, folliculogenesis is the maturation of the ovarian follicle, a densely packed shell of somatic cells that contains an immature oocyte. Folliculogenesis describes the progression of a number of small primordial follicles into large preovulatory follicles that enter the menstrual cycle.

Contrary to male spermatogenesis, which can last indefinitely, folliculogenesis ends when the remaining follicles in the ovaries are incapable of responding to the hormonal cues that previously recruited some follicles to mature. This depletion in follicle supply signals the beginning of menopause.

Menstruation(SHORT)

Menstruation is the periodic discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. This cyclic discharge is seen in females of certain mammalian species (including humans). It begins with the onset of menarche at or before sexual maturity and stops at or near menopause (commonly considered the end of a female's reproductive life). The periodicity of menstruation gives rise to commonly used euphemisms such as "period" and "monthly".

Women typically stop menstruating if they conceive or if they are breastfeeding. When menstruation stops for longer than about 90 days in the absence of pregnancy or breastfeeding, a medical evaluation should occur, as a number of health problems can result in absent menstruation. Menstruation lasts from puberty until menopause among non-pregnant women.

Movement of Oxygen and Carbon Dioxide

lveoli for efficient gas exchange.

TERMS

oxyhaemoglobin
the form of hemoglobin, loosely combined with oxygen, present in arterial and capillary blood

hemoglobin
iron-containing substance in red blood cells that transports oxygen from the lungs to the rest of the body; it consists of a protein (globulin) and heme (a porphyrin ring with iron at its center)

partial pressure
the pressure one component of a mixture of gases would contribute to the total pressure

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Basic Principles of Gas Exchange

The structure and organization of the lung is meant to maximize its surface area to increase gas diffusion. Due to the enormous number of alveoli (approximately 300 million in each human lung), the surface area of the lung is very large (75 m2). Having such a large surface area increases the amount of gas that can diffuse into and out of the lungs.

Gas exchange during respiration occurs primarily through diffusion: a process in which transport is driven by a concentration gradient and molecules will move from a region of high concentration to a region of low concentration. Gas exchange between the air within the alveoli and the pulmonary capillaries occurs by diffusion . The oxygen must first dissolve before passing through the respiratory epithelium. Gas moves from a region of high partial pressure to a region of low partial pressure, down a partial pressure gradient. Partial pressure (P) is a measure of the concentration of the individual components in a mixture of gases. The total pressure exerted by the mixture is the sum of the partial pressures of the components in the mixture. The rate of diffusion of a gas is proportional to its partial pressure within the total gas mixture.  The distance between the blood and the air within the alveoli is approximately 0.7 micrometers. This distance is decreased during inhalation as the lung distends, allowing extremely fast and efficient diffusion across this tiny distance. The various factors that affect gas exchange include oxygen, carbon dioxide, and the ventilation/perfusion (V/Q) ratio.

Gas exchange
Gas exchange
This schematic demonstrates how gas is exchanged in humans between a capillary and an alveolus.
Oxygen
The partial pressure of oxygen (PO2) is always lower in the alveoli compared to the external environment due to the continuous diffusion of oxygen across the alveolar wall along with the 'diluting' effect of CO2 entering the alveoli as it is travels in the opposite direction to the O2. The PO2 in the alveoli is still higher than that in the capillaries, so oxygen diffuses into the blood. Once through the alveolar and capillary walls, the oxygen combines with hemoglobin to form oxyhaemoglobin that is transported within the bloodstream.

Carbon Dioxide
Carbon dioxide enters the red blood cell as a waste product from cells, which reacts with water to form carbonic acid (CA). CA dissociates to bicarbonate ions and hydrogen ions. These diffuse into plasma, where H+ are buffered by hemoglobin. Approximately 5% of the total body CO2 dissolves in the plasma, 5% is carried as carboxyhaemoglobin on proteins, and 90% is carried as bicarbonate ions in the plasma. The partial pressure of carbon dioxide (PCO2) in the capillaries is higher than that in the alveoli, thus CO2 diffuses into the alveoli where it is exhaled.

V/Q Ratio
The adequacy of pulmonary gas exchange relies on the V/Q ratio (ventilation/perfusion ratio). The alveoli should receive the ideal amounts of blood and gas for gas exchange. In disease situations, the amount of air delivered may be reduced, the alveolar wall may be thickened, or the alveolar surface area may be reduced with the result that less gas is able to diffuse out of the alveolus. Alternatively, blood supply may be impaired so that, despite sufficient ventilation, insufficient exchange occurs to support the body.

Mutations

In genetics, a mutation is a permanent change of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal genetic element. Mutations result from unrepaired damage to DNA or to RNA genomes (typically caused by radiation or chemical mutagens), errors in the process of replication, or from the insertion or deletion of segments of DNA by mobile genetic elements. Mutations may or may not produce discernible changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, cancer, and the development of the immune system.

Mutation can result in several different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Mutations can also occur in nongenic regions. One study on genetic variations between different species of Drosophila suggests that, if a mutation changes a protein produced by a gene, the result is likely to be harmful, with an estimated 70 percent of amino acid polymorphisms that have damaging effects, and the remainder being either neutral or weakly beneficial. Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent or correct (revert the mutated sequence back to its original state) mutations

Oogenesis

Oogenesis, ovogenesis, or oögenesis /ˌoʊ.əˈdʒɛnɨsɪs/ is the creation of an ovum (egg cell). It is the female form of gametogenesis; the male equivalent is spermatogenesis. It involves the development of the various stages of the immature ovum

Oogenesis in mammals

Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. (In mammals, the first polar body normally disintegrates before dividing, so only two polar bodies are produced.)
In mammals, the first part of oogenesis starts in the germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary.

Note that this process, important to all animal life cycles yet unlike all other instances of cell division, occurs completely without the aid of oo spindle-coordinating centrosomes.

Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper). Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes.

Cell type ploidy Process Process completion
Oogonium diploid Oocytogenesis (mitosis) third trimester (forming oocytes)
primary Oocyte diploid Ootidogenesis (meiosis 1) (Folliculogenesis) Dictyate in prophase I for up to 50 years
secondary Oocyte haploid Ootidogenesis (meiosis 2) Halted in metaphase II until fertilization
Ovum haploid
Oogonium —(Oocytogenesis)—> Primary Oocyte —(Meiosis I)—> First Polar Body (Discarded afterward) + Secondary oocyte —(Meiosis II)—> Second Polar Body (Discarded afterward) + Ovum

The creation of oogonia
The creation of oogonia traditionally doesn't belong to oogenesis proper, but, instead, to the common process of gametogenesis, which, in the female human, begins with the processes of folliculogenesis, oocytogenesis, and ootidogenesis.

Human oogenesis
At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated FSH to form secondary follicles. The primary follicles have formed from primordial follicles, which developed in the ovary at around 10–30 weeks after conception. By around day 9 of the cycle, only one healthy secondary follicle remains, with the rest having undergone ovarian follicle atresia. The remaining follicle is called the dominant follicle and is responsible for producing large amounts of estradiol during the late follicular phase. Estradiol production depends upon co-operation between the theca and granulosa cells. On day 14 of the cycle, an LH surge occurs, which itself is triggered by the positive feedback of estradiol. This causes the secondary follicle to develop into a tertiary follicle, which then ovulates some 24–36 hours later. An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte. The empty follicle then forms a corpus luteum, which later releases the hormone progesterone.

Oocytogenesis[edit]
Oogenesis starts with the process of developing oogonia, which occurs via the transformation of primordial follicles into primary oocytes, a process called oocytogenesis. Oocytogenesis is complete either before or shortly after birth.

Number of primary oocytes[edit]
It is commonly believed that, when oocytogenesis is complete, no additional primary oocytes are created, in contrast to the male process of spermatogenesis, where gametocytes are continuously created. In other words, primary oocytes reach their maximum development at ~20[5] weeks of gestational age, when approximately seven million primary oocytes have been created; however, at birth, this number has already been reduced to approximately 1-2 million.

Recently, however, two publications have challenged the belief that a finite number of oocytes are set around the time of birth.The renewal of ovarian follicles from germline stem cells (originating from bone marrow and peripheral blood) has been reported in the postnatal mouse ovary.

Due to the revolutionary nature of these claims, further experiments are required to determine the true dynamics of small follicle formation.

Ootidogenesis
The succeeding phase of ootidogenesis occurs when the primary oocyte develops into an ootid. This is achieved by the process of meiosis. In fact, a primary oocyte is, by its biological definition, a cell whose primary function is to divide by the process of meiosis.

However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have halted at this stage of development, called the dictyate. After menarche, these cells then continue to develop, although only a few do so every menstrual cycle.

Meiosis I
Meiosis I of ootidogenesis begins during embryonic development, but halts in the diplotene stage of prophase I until puberty. The mouse oocyte in the dictyate (prolonged diplotene) stage actively repairs DNA damage, whereas DNA repair is not detectable in the pre-dictyate (leptotene, zygotene and pachytene) stages of meiosis. For those primary oocytes that continue to develop in each menstrual cycle, however, synapsis occurs and tetrads form, enabling chromosomal crossover to occur. As a result of meiosis I, the primary oocyte has now developed into the secondary oocyte and the first polar body.

Meiosis II
Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this process is also halted at the metaphase II stage until fertilization, if such should ever occur. When meiosis II has completed, an ootid and another polar body have now been created.

Folliculogenesis
Main article: Folliculogenesis
Synchronously with ootidogenesis, the ovarian follicle surrounding the ootid has developed from a primordial follicle to a preovulatory one.

Maturation into ovum
Both polar bodies disintegrate at the end of Meiosis II, leaving only the ootid, which then eventually undergoes maturation into a mature ovum.

The function of forming polar bodies is to discard the extra haploid sets of chromosomes that have resulted as a consequence of meiosis.

In vitro maturation
Main article: In vitro maturation
In vitro maturation (IVM) is the technique of letting ovarian follicles mature in vitro. It can potentially be performed before an IVF. In such cases, ovarian hyperstimulation isn't essential. Rather, oocytes can mature outside the body prior to IVF. Hence, no (or at least a lower dose of) gonadotropins have to be injected in the body. However, there still isn't enough evidence to prove the effectiveness and security of the technique.

Oogenesis in non-mammals
Main article: Evolution of sexual reproduction
Many protists produce egg cells in structures termed archegonia. Some algae and the oomycetes produce eggs in oogonia. In the brown alga Fucus, all four egg cells survive oogenesis, which is an exception to the rule that generally only one product of female meiosis survives to maturity.

In plants, oogenesis occurs inside the female gametophyte via mitosis. In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia. In flowering plants, the female gametophyte has been reduced to an eight-celled embryo sac within the ovule inside the ovary of the flower. Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule.

In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the estrus cycle.

Parathyroid Hormone

Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the thyroid gland) acts to decrease calcium concentration. PTH acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor (high levels in bone and kidney) and the parathyroid hormone 2 receptor (high levels in the central nervous system, pancreas, testis, and placenta). PTH half-life is approximately 4 minutes. It has a molecular mass of 9.4 kDa