Pcat Endocrinology

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CHEMICAL REGULATION IN ANIMALS

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means of internal communication, coordinating the activities of the organ systems

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Glands

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synthesize or secrete hormones

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Adrenal Glands

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on top of the kidneys, and consist of the adrenal cortex and the adrenal medulla

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Adrenal Cortex

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in response to stress, the adrenocortiotropic hormone (ACTH), produced by the anterior pituitary, stimulates the adrenal cortex to produce more adrenocortical steroids or corticosteriods, which are bound to transport proteins called transcortins in the blood stream.

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Glucocorticoids

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- such as cortisol and cortisone, are involved in glucose regulation and protein metabolism
-raise blood glucose levels by promoting protein breakdown, and gluconeogenesis and decreasing protein syntesis
-increase plasma glucose levels and are antogonistic to insulin
-release amino acids from skeletal muscle and lipids from adipose tissue
-promote peripheral use of lipids and have antiflammatory effects

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Mineralocorticoids

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-i.e. aldosterone, regulate plasma level of sodium and potassium, and extracellular water volume
-causes active reabsorption of sodium and water in the nephron and increases blood volume, and blood pressure
-stimulated by angiotensin II and inhibited by ANP

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Cortical sex hormones

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secretes small quantities of androgens like androstendione and dehydroepiandrosterone

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Adrenal Medulla

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produces epinephrine (adreinaline) and norepinephrene

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Epinephrine

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increases the concersion of glycogen in liver and muscle tissue, causing an increase in blood glucose levels and inceres in the basal metabolic rate
-increase the rate and strength of the heartbeat and dilate to constrict blood vessels to increase blood supply except to kidney, skin, and digestive tract
-promote the release of lipids by adipose tissue

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नीडः
nīḍa

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nest

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Pituitary Gland

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-(hypophysis) small trilobed gland lying at the base of the brain
-main lobes anterior and posterior,
3rd lobe rudimentary
-hangs below the hypothalamus and connected by infudibulum

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Anterior pituitary

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synthesizes hormones to directly stimulate target organs and tropic hormones which stimulate other endocrine glands to release hormones
-secretions regulated by hypothalamic secretions called releasing/inhibiting hormones/factors

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Growth (Direct) Horomone (GH, somatropin)

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-promotes bone and muscle growth, protein synthesis and lipid mobilization and catabolism.
-deficiency: dwarfism
-overproduction: giantism

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Prolactin (Direct Hormone)

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stimulates milk production and secretion of female mammary glands

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Adrenocorticotropic hormone (ACTH)

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stimulates adrenal cortex to sythesize and secrete glucocorticoids, and regulated by corticotrophin-relasing factor (CRF)

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Thyroid-stimulating (tropic) hormone (TSH)

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stimulates the thyroid gland to synthesize and release thyroid hormones, including thryroxin

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Luteinizing (Tropic) Hormone (LH)

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in women stimulates ovulation and formation of the corpus luteum, and responsible for regulating progesterone secretion in women. In men stimulates the interstitial cells of the testes to synthesize testosterone.

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Follicle-stimulating (Tropic) hormone (FSH)

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causes maturation of ovarian follicles that begin secreting estrogen; in men, stimulates maturation of the seminiferous tubules and sperm production.

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Melanocyte-stimulating (Tropic) hormone (MSH)

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-secreted by the intermediate lobe of the pituitary.
-function unclear in mammals, but in frogs, causes darkening of the skin via induced dispersion of the molecules of pigment in the melanophore cells.

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दुःखम्
duḥkham

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unhappiness, sorrow, pain

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Posterior pituitary

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(neurohypophysis) does not synthesize hormones; it stores and releases the peptide hormones oxytocin and ADH produced by neurosecretory cells o the hypothalamus.

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Oxytocin

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-secreted during childbirth, increases the strength and frequency or uterine muscle contractions
-induced by suckling and stimulates milk secretion in the mammary glands

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Antidiuretic hormone (ADH; vasopressin)

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-increases the permeability of the nephron's collecting duct to water promoting water reabsorption and increasing blood volume= increase blood pressure
-secreted when plasma osmolarity increases, as sensed by osmoreceptors in the hypothalamus, or when blood volume decreasess sensed by baroreceptors in the circulatory system

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Hypothalamus

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-part of the forebrain and is located directly above the pituitary gland
-recieves neutral transmissions from the other parts of the brain and from the peripheral nerves that trigger speciic repsonses from neurosecretory cells

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Neurosecretory Cells

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regulate the pituitary gland secretions via negative feedback mechanism and actions of inhibiting and releasing hormones

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Hypothalamus & Anterior pituitary Interactions

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Hypothalamic-releasing hormones stimulate or inhibit the secretions of the anterior pituitary
GnRH stimulates the anterior pituitary to secrete FSH and LH. Releasing hormones are secreted into the hypothalamic-hypophyseal portal system, and blood from the capillary bed in the hypothalamus flows through a portal vein into the anterior pituitary and diverges into a second capillary network
feedback system regulates the secretions of the endocrine system
-plasma levels of adrenal cortical hormones drop, hypothalamic cells release ACTH-releasing factor (ACTH-RF) into the portal system
-plasma concentration of the corticosteroids exceeds the normal plasma level steroids exert inhibitory effects on the hypothalamus

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Hypothalamus & Posterior pituitary Interactions

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Neurosecretory cells in the hypothalamus sunthesize both oxytocin and ADH and transport them via their axons into the posterior pituitary for storage and secretion

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Thyroid

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-has hormones that affect the function of nearly every organ system in the body
-essential for growth and development in children
-maintenance of metabolic activity in adults

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Thyroid Hormones

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Thyroxine (T4) and Triidothryronine (T3) are formed of glycoprotein hyroglobulin synthesized in the thyroid cell
-iodinated tryosine residues preseint in thryroglobulin are able to bind together to form active thyroid hormones because of tertiary structure of the glycoprotein

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Thyroxine (T3) & Triiodothyronin (T4)

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-derived from the iodination of the amino acid tryosine
-hypothyroidism: under secreted or not secreted at all= slowed heart and respiratory rate, and weight gain= cretinism in infants (mental retardation
-hyperthryroidism: over secretion of thyroid hormone- increased metabolic rated, feelings of excessive warmth, and weight loss
-both result in goiter (thyroid enlargement/bulge)

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Calcitonin

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decreases plasma Ca2+ concentration by inhibiting the relase of Ca2+ from the bond
regulated by plasma Ca2+ levels
antagonistic to the parathyroid hormone

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Pancreas

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both exocrine organ and endocrine organ
exocrine function performed by the cells that secrete digestive enzyme into the small intesine via ducts
endocrine function is performed by small gladulare structers called the islets of Langerhands composed of alpha and beta cells.

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Alpha cells

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produces and secrete glucagon

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Beta cells

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produce and secrete insulin

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Glucagon

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stimulates protein and fat degradation, the conversion of glycogen to glucose, and glucogenosis which serve to increase blood glucose levels
-antagonistic to insulin

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Insulin

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a protein hormone secreted in response to a high blood glucose concentration
-stimulates uptake of glucose by muscle and adipose cells and the storage as glucose as glycogen
-stimulates the sythesis of fats from glucose and the uptake of amino acids
-antagonistic to glucagona nd glucoorticoids
-underproduction= hyperglycemia=high blood glucose levels

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Parathyroid Glands

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four small pea-shaped structures embedded in the posterior surface of the thyroid
-synthesize and secrete parathyroid hormone (PTH)-regulates plama Ca2+ concentration
-stimulate Ca2+ from bone and decrease Ca2+ excretion in the kidneys

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Kidneys

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produce renin when blood volume falls to restore it by increasing sodium reabsorption at the kidney, leading to an increase in water
-produce erythroprotein (EPO):glycoprotein that stimulates red blood cell production (stem cell differentiation)

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Gastrointestinal Hormones

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Ingested food stimulates the stomach to release the hormone gastrin is then carried to the gastric gland and stimulate to secrete HCl
Secretin is relased by the small intestine when acidic food material enters the stomach- nutralizes acitiy of the chyme
Hormone cholecystokinin released by the small intestine in response to the presence of fats and causes the contraction of the gallbladder and release of bile

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Pineal Gland

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tiny structure at the base of the brain that secrets the hormone melatonin- play a role in regulation of circadian rhythms (light and dark cycles)

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MECHANISM OF HORMONE ACTION

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two ways hormones affect the activities of their target cells; via extracellular receptors or intracellular receptors

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Peptides hormones

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range from short peptides (ADH), to complex polypeptides (insulin)
-binding to specific receptors on the surface of their target cells triggers a series of enzymatic reactions within each cell
-cascade effect: with each step the hormone effects are amplified.

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Steroids

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estrogen and aldosterone
-receptor-hormone complex enters the nucleus and dierectly acitvates the expressoin of specific genes by binding to receptors on chromatin which induces a change in mRNA transcription and protein synthesis

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REGULATION IN PLANTS

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plant hormones are primarily involved in the regulation of growth
produces by actively growing parts of the plant like meristematic tissues in the apical region of shoots and roots

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Auxins

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important class of plant hormones associated with several types of growth patterns
responsible for phototrotropism which is the tendency for the shoots of plants to bend towards light
Indole-acetic acid hormone associated with phototropism

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Geotropoism

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the growth of plants toward or away from gravity
negative: causes shoots to grow upward away from gravity
positive: causes roots to grow toward the pull of gravity

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Gibberellins

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stimulate rapid stem elongatoin in plants that normally do not grow tall- inhibit new roots and promote phloem cells by the cambium

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Kinins

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promote cell division- type of cytokinin
action of kinetin is enhanced when auxin is present

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Ethylene

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stimulates fruits ripening and induces senescene or aging

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Inhibitors

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block cell division and serve an important role in growth regulation
important in maintenence of dormancy in lateral buds and seeds of plants

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Antiauxins

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regulate activity of auxins
-indoleacetic acid oxidase regulate the concentration of indoleascetic acid