Medical Physiology Lectures - Endocrine & Reproductive Systems PDF

Medical physiology Lectures Of Endocrine System & Reproductive Physiology. Uruk university Health and medical technology college Anesthesia technology dept. DR.RAAD H.H. 1  Coordination of body functions: The activities...

Medical physiology Lectures Of Endocrine System & Reproductive Physiology. Uruk university Health and medical technology college Anesthesia technology dept. DR.RAAD H.H. 1  Coordination of body functions: The activities of cells & organs are coordinated & controllrd by specifically interaction of nervous system & hormonal or endocrine system through releasing secreations of : 1. Neurotransmitters secreted by neurons axon terminals in synaptic junctions & act locally on cell functions. 2. Endocrine hormones secreted by glands in blood & act on cells in another location of the body. 3. Neuroeniondocrine hormones secreted by neurons in blood & act on cells at another location in body. 4. Paracrine hormone or substance secreted by cells into extracellular fluid & affect neighboring cells of a different type. 5.Autocrines hormone or substance secreted by cells into extracellular fluid & act on function of same cells that produced them. 6. Cytokines (e.g interleukins) are peptides secreted by cells into extracellular fluid & functions as autocrines, paracrines, or endocrine hormones. 2  Target tissue cells types are : The Endocrine Hormones carried by blood to cells of body called The Target tissue cells have special receptor for the action of the hormone. Target tissue cells types are : 1- Many different types of cells of body; e.g. Growth Hormone. 2- Only specific target tissues, E.g. Adrenocorticotropic Hormone (ACTH). After hormones secreted , small parts circulates freely & major part will bind to plasma proteins which act as: 1- Storage site of hormones. 2- Buffer mechanism of specific hormones. Endocrine glands : defined as ductless glands, releases their products direct to blood circulation & its products called hormones. Hormones the “chemical messengers” : defined as chemical substances produced by glands or neurosecretory cells (so not all the hormones are secreted by endocrine glands e.g. GIT hormones) released into the blood in response to a specific stimulus. 3  Chemical Structure of Hormones; There are 3 general classes : 1. Proteins & polypeptides: secreted by Anterior & Posterior Pituitary gland, Pancreas (Insulin & Glucagon), Parathyroid hormone & others. 2. Steroids : secreted by Adrenal Cortex (cortisol & aldosterone), Ovaries (Estrogen & Progesterone), Testes (Testosterone). 3. Amino Acid Derivatives of the Tyrosine: secreted by Thyroid (Thyroxine & Triiodothyronine) &Adrenal Medullae (Epinephrine & Norepinephrine). 4.Glycoprotein. Time Onset of Hormone Secretion : Some hormones, are secreted within seconds after gland stimulated ; such as norepinephrine & epinephrine, Other hormones actions may require months for full effect , such as thyroxin or growth hormone. 4  Functional classification of hormones: Hormones are classified into two functional categories: 1.Trophic hormones 2. Nontrophic hormones A trophic hormone: Acts on another endocrine gland to stimulate secretion of its hormone. E.g. (TSH), stimulates the secretion of thyroid hormones. hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. A Non-trophic hormone: acts on nonendocrine target tissues. For e.g., parathormone scretedfrom parathyroid glands acts on bone tissue to stimulate the release of calcium into blood. Aldosterone released from cortical region of the adrenal glands acts on the kidney to stimulate the reabsorption of sodium into the blood. 5 Mechanisms of hormonal secretion control : (A) Feedback mechanism: 1-negative Feedback Mechanism: a- Direct negative feedback: It relates to rate of release of hormone concentration in blood. e.g.: ACTH (adrenocorticotrophic hormone) b- Indirect negative feedback: This type will act when the nervous system (Hypothalamus) is involved in the process: e.g.: So ACTH affects release of cortisol via CRH (indirect feedback) by cortisol increasing level. C- Short negative feedback: So called short feedback because the distance between the hypothalamus & the pituitary is short. E.g. (GHRH) stimulates secretion of (GH ) which affect all body tissues & there is no hormone released in response to it (no target gland). 6  (B)Influence of the nervous system : The glands that are primarily controlled by the nervous system are: (1) Adrenal medulla. ( 2)Posterior lobe of the pituitary gland. 2- Positiove Feedback Mechanism: An increase secretion of particular hormone from a specific gland in response to the increase in chemical substance. e.g. FSH (follicular stimulating hormone) secreted by Pituitary gland ,circulates in blood to affect ovary in female. Cyclical Variations of hormones : is a periodic variations in hormone secretion that are influenced by seasonal changes, various stages of development & aging & the diurnal (daily) cycle & sleep, E.g. secretion of GRTH is markedly increased during early period of sleep but is reduced during later stages of sleep. 7  Mechanism action of hormones: So how does the hormone act? When the hormone bindes with its receptor, this usually initiates a cascade of reactions in the cell. The first step of a hormone’s action is to bind to specific receptors at target cell, after dissociation of binding protein. Note : Shape of the receptor is important e.g Feminizing Testis case (the male has normal testes secret testosterone, but there are no receptors for it so there is absence of secondary sex characteristics & organs. The locations of hormone’s receptors, are generally : 1. In or on the surface of cell membrane : mostly for protein, peptide & catecholamine hormones. 2. In the cell cytoplasm : found mainly in cytoplasm receptors for different steroid hormones. 3. In the cell nucleus : Receptors for thyroid hormones are found in nucleus & are believed to be located in direct association with one or more of chromosomes. 8  Regulation of number & sensitivity of hormone receptors: No. of receptors in a target cell usually varies daily, or even at minute. Types are: Down-regulation receptors: the number of active receptors decreases due to increasing hormone concen. & increased binding with its target cell receptors. Up-regulation receptors : Some stimulating hormone are greater than normal formation of receptor. 9  Pituitary Hormones &Their Control by the Hypothalamus: The hypothalamus :is composed of nervous tissue situated below Thalamus & has efferent fibers connecting it to the rest of CNS. The synthesis & storage of chemical substances occur within a specific nerve cells & its secretion occur closely with blood vessels , so we could use the terms ‘’Neurosecretion or Hormone’’ on them. Most of the hypothalamic nuclei axon terminate in posterior lobe of pituitary gland. The excretion of any releasing or inhibiting hormones from the hypothalamus is controlled by nervous & partly by endocrine feedback mechanism. 10  The hypothalamus contains several types of neurons that release different hormones; which are : 1- Thyrtrophin releasing hormone (TRH). 2- Corticotrophin releasing hormone (CRH). 3- Somatostatin or Growth hormone inhibiting hormone (GHIH). 4- Somatrophin releasing hormone or Growth hormone releasing hormone (GHRH). 5- Melanocyte stimulating hormone releasing hormone. 6- Gonadotrophin releasing hormone (GnRH) 7- Prolactin inhibiting factor (PIH) (no milk secretion in normal conditions because of this factor). 11  Anther classification of hypothalamus hormones depend on function: There are two types of hormones secreted by the hypothalamus they are: 1. Releasing hormones : e.g. Gonadotrophin-releasing hormone (GnRH) , Thyrotrophin-releasing hormone (TRH). , Somatotropin-releasing hormone (GHRH) & Adrenocorticotrophin-releasing hormone. 2. Inhibiting hormones: e.g. Somatostatin or Growth-inhibiting hormone (GHIH) & Melanocyte-inhibiting hormone. 12  Pituitary gland (Hypophysis) also called ‘’The Master Gland ‘’: lies in the ‘’ Sella Turcica ‘’, at the base of the brain ; it is made up of two functionally active lobes called : Anterior lobe (Adenohypophysis) & Posterior lobe (Neurohypophysis) &There is Intermediate lobe. The anterior lobe secretes about 80% of hormones, which are under control of hormones secreted from hypothalamus. Hypothalamus nerves signals controls the Secretions of the posterior pituitary lobe. In contrast, hypothalamic releasing & hypothalamic inhibitory hormones controlling secretions of the anterior pituitary lobe. 13 14 15  The hormones of the anterior pituitary gland: Growth hormone- GH Adrenocorticotropin –ACTH (corticotrophin). Thyroid-stimulating hormone-TSH (Thyrotropin). Prolactin promotes mammary gland development & milk production. ICSH :stimulate testosterone production from interstitial cells of testis. MSH :Promote distribution of Melanin granules. (2) Gonadotropic hormones, follicle-stimulating hormone FSH & luteinizing hormone LH. The 2 hormones secreted by the posterior pituitary gland:.Antidiuretic hormone – ADH (also called Vasopressin). Oxytocin. 16  Hormones of the posterior lobe of the pituitary gland: are Oxytocin & vasopressin they are typical ‘’Neural Hormones’’. ‘’Antidiuretic Hormone (ADH) or Vasopressin’’: ADH stimulate reabsorption of water from tubules & specifically collecting ducts of kidney, ; act as Antidiuresis. 17  Control of ADH hormone secretion; 1- Plasma osmolarity: 2- Blood volume: e.g blood loss (hemorrhage). Decreased stretch of the Baroreceptors (called volume or low pressure receptors ) of the carotid, aortic & pulmonary regions stimulates ADH secretion. 3-Variety of stimuli: Drugs e.g. morphine, pethedine (tranquilizers) centrally acting & stimulate release of ADH→ increase of reabsorption of water & decrease in volume of water excreted to outside body. 4-Alcohol : inhibits secretion of ADH & increase urination (so drunk people urinate a lot). 5. Blood pressure. 18  Clinical conditions due to disturbances in ADH : Polyuria :After car accidents a decrease in secretion of ADH & resulted increase urination. D.I. (Diabetes Insipidus) : presented in 2 types : Central D.I. : Tumor of the pituitary gland→ decrease ADH secretion. Nephrogenic D.I.; differentiation between D.I. & D.M. (diabetes mellitus) in D.M. there is polyuria &polydipsia & specific gravity of urine is higher because of the presence of glucose. Congenital absence of ADH receptors in the kidney, so high level of ADH but no response. 19  Oxytocine: Oxytocin is presents in male & female but its exact physiological action is not obvious in male. Its action in females is on both : 1. Effects on uterus; It causes contraction of uterus at labor. It aids in expulsion of fetus &placenta. 2-Effects on mammary gland: ‘’The Milk Ejection Reflex’’ Oxytocin In lactation, causes milk to be ejected from the breast for the baby to suckling it , so oxytocin causes ejection of milk not secretion of it , because the secretion is under the effect of prolactin; (It is a Neurohormonal Reflex). Also sound or sight of the baby stimulate release of milk, while stress inhibits release of oxytocin, that leads to reduced milk flow. 20  Anterior Pituitary Hormones ; Could be Classified as groups : 1-Glycoproteins: TSH, LH, FSH ,Human Chorionic Gonadotropins (HCG) secreted during pregnancy from the placenta. 2-Somatomammotrophins: (Single Peptide) Prolactin & Growth Hormone, Human Placental Lactogen (HPL). 3- ACTH related peptide. peptides derived from parent compound known as (Big ACTH). 21  TSH (Thyroid Stimulating Hormone) : TSH is a glycoprotein synthesized & stored in the Thyrotroph cells, its primary function is on the thyroid gland. Stimulate the synthesis & release of T3 & T4 after several mechanisms : 1. Stimulation of iodide pumps in the cell membranes. 2. stimulates the synthesis of thyroid storage protein which is ‘’Thyroglobulin’’. 3. Stimulates the synthesis of T3 &T 4. 4. Stimulates the secretion of T3 & T4 from the thyroglobulin complex. 5. If there is over secretion of TSH there is an enlargement of the thyroid gland. 22  FSH (follicle stimulating hormone) & LH (lutenizing hormone): They are glycoproteins hormons synthesized by gonadotrophs. They are responsible for development of the ovarian follicles & ovulation. The production of LHRH (lutenizing hormone releasing hormone) is inhibited by estrogen & progesterone; this phenomenon is used in the contraceptive pills, While LHRH is stimulated by estrogen deficiency, so we can use antiestrogenic drugs like clomid. 23  In male FSH stimulates the development of sperms i.e. spermatogenesis, Inhibin an a peptide , feeds back & inhibit secretion of FSH. LH in male :it is also called interstitial cell stimulating hormone (ICSH), stimulates the interstitial cells to synthesize & secretion of Testosterone. As the level of testosterone increase, we have inhibition of LH secretion 24  Growth hormone (GH): Its function effects directly on all or almost all tissues of the body. It effect the metabolism & tissue growth. Its effect on metabolism is a direct, but on growth is indirect via a peptide called Somatomedin. Somatomedin is peptide humeral factor synthesized in the liver & to lesser extent by kidney under effect of growth hormone. Effects of GH on metabolism: 1-Effect on proteins: increases protein. 2-Effect on fat metabolism : increase release of fatty acids & utilization of energy from fat; also increase Keton Bodies formation by liver (Ketogenic hormone). 25  3- Effect on carbohydrates: (a) increased glucose production by the liver. (b) increased insulin secretion; This will cause increase in blood glucose concen.. So it is considered as a (Diabetogenic hormone). 4- Effect on electrolytes: It decreases elimination of electrolytes from the body & It increases absorption of calcium by intestine. 5-Effect on growth: Increase size of body by increase protein deposition & reproduction of chondrocytic & osteogenic cells for bone growth. GH stimulates a humeral factor called ‘’Somatomedine’’ acts on cartilage & it is synthesized in liver & kidney. The Somatomedins also called Insulin-like Growth Factors ( IGFS ) due to its many effects on growth which are similar to effects of insulin on growth. 26  Abnormalities of Growth Hormone Secretion: 1. Reduction in GH secretion : ‘Panhypopituitarism’: a tumor decreasing all the pituitary hormones. ‘Dwarfism’: deficiency of GH during childhood. 1. Increase in GH secretion: 1-Gigantism: Due to large quantities of GH before adolescence; person’s height increases & becomes a giant. 2-Acromegaly: Due to large quantities of GH after adolescence ; person cannot grow taller, but have thicker & enlarged bones of hands , feet , membranous bones, cranium, & vertebrae, Many soft tissue organs, e.g. tongue, liver &kidneys, are greatly enlarged. 27  Prolactin hormone: It is secreted by lactotroph cells. In female it causes milk secretion. During pregnancy no prolactin secretion because of estrogen & progesterone secreted by placenta plus prolactin inhibiting factor. After delivery the effect of estrogen & progesterone diminished , therefore prolactin causing milk secretion. Pathologically : Sometimes an increase in prolactin leads to inhibition of LH & FSH → estrogen &progesterone inhibition → amenorrhea (no menstrual cycle). In case of dead fetus, we don’t need milk so we give Antiprolactin drugs e.g. (Parlodel). 28  Thyroid gland & its hormones : The thyroid secretes : Secretes Two ( 2 ) major hormones ( Thyroxine T4) , Tetraiodothyronin & (T 3) Triiodothyronine , responsible for body metabolism & secretes Calcitonin hormone , for calcium metabolism. Thyroid gland has a characteristic feature of trapping iodide from the circulation. Thyroid gland hormones is controlled by TSH. The physiological action of thyroid hormone: 1- increases transcription of large numbers of Genes; 2- increases cellular metabolic activity: by Increase number & activity of mitochondria & Increases formation of (ATP). & Increase the activity of enzyme Na+-K+- ATPase, which increases heat production. Basal metabolic rate ‘BMR’ is the quantity of energy production at rest during optimal temperature, measured 12 hours after last meal. 29  3-Calorigenic Action: T4 &T3 increases O2 consumption & heat production 4-Effect on carbohydrates , fat & protein: It stimulates glycolysis, hepatic gluconeogenesis & increase in blood glucose. 5 - Effect on the Cardiovascular System: Increases Blood Flow & Cardiac & heart rate increases greatly. Effect on respiration: Increases utilization of O2 due to increases rate of metabolism & formation of CO2. Effect on GIT: increase absorption of food stuffs & increase in rate of secretion of digestive juices & increase motility of GIT. Excessive thyroid hormone results in diarrhea & associated with increase appetite due to increase of BMR (Basal Metabolic Rate). 30  Effect on Protein: it stimulates the synthesis of specific proteins ;By Anabolic action when TH is within the physiological limits. But if there is increase in level of thyroid hormone , the anabolic will turn to Catabolic action, especially in muscles & causes muscle weakness (‘’Thyrotoxic Myopathy’’). Increases plasma Creatinine & amino acids in blood (‘’Creatinurea’’). In Hypothyroidism , there will be deposition of mucoprotein S/C which sucks water & causes swelling (edema) which is differ from congestive heart failure edema because it is not pitting. Effect on Vitamins, causes increased need for vitamins. Effect on sexual function: low of thyroid hormone In men, cause loss of libido. low of thyroid hormone often causes Menorrhagia & Polymenorrhea. A Hypothyroid woman & man, have decreased libido ; Also Oligomenorrhea & Amenorrhea. 31  Effect on Sleep: Hyperthyroid person has feeling of tiredness, but because of excitable effects of thyroid hormone causing difficulty to sleep ;Conversely, extreme sleeping is characteristic sign of hypothyroidism. Effect on growth (effect on the bone): Thyroid hormones are essential for normal growth & skeletal maturation. In Congenital hypothyroidism , bone growth & epiphysial closure are delayed. Effect on the CNS : promotes growth & development of the brain. Hyperthyroid person shows signs of nervousness,, exaggerated response to environmental stimuli & many psychoneurotic tendencies, e.g. anxiety complexes, worry & paranoia (always suspect). Effect on Other Endocrine Glands: Increases rates of secretion of most endocrine glands & also increases tissues need for hormones. e.g increases rate of glucose metabolism everywhere in the body & therefore causes a need for increased insulin secretion by the pancreas. 32  (Clinical conditions) : Goiter : is Enlargement of the thyroid gland for any reason. The thyroid gland Functionally types is either increased or decreased activity (Hyper or Hypothyroidism). Goiter types : Endemic goiter : Usually found in places of insufficient iodine in food. Idiopathic Nontoxic Colloid Goiter: The thyroid gland enlarged with no disturbance in the thyroid function. Most of these patients show signs of Mild Thyroiditis. 33  Myxedema : an edematous appearance throughout the body developed in severe cases of hypothyroidism. Cretinism disease defined as : It is caused by sever hypothyroidism during fetal life, infancy, or childhood. It is characterized by failure of body growth & by mental retardation. Cretinism signs of short stature & mental retardation, differentiated from GH deficiency that is short stature but without mental retardation. 34  Hyperthyroidism : An Excessive thyroid secretion diseases: In Hyperthyroidism, the level of TSH is reduced, but it is not lead to reduction in thyroid hormone. Symptoms of Hyperthyroidism: (1) Excitability (2) Intolerance to heat (3) Increased sweating (4) Mild to extreme weight loss (5) Varying degrees of diarrhea, increase appetite (6) Muscle weakness (7) Nervousness or other Psychic disorders (8) extreme fatigue but inability to sleep (9) Tremor of the hands (10) Vitamin deficiency D. Thyroid Adenoma: Hyperthyroidism occasionally results from a localized adenoma (a tumor) that develops in the Thyroid tissue & secretes large amounts of thyroid hormone. Fine muscle tremor: Typically fine small action tremor in both hands & fingers; generally not caused by a neurological disease but by reaction to certain drugs, alcohol withdrawal, or Hyperthyroidism & hypoglycemia. Exophthalmos : The protrusion of one or both eyes anteriorly out of the orbit within the rigid bony orbit. commonly manifests in thyroid-associated eye disease e.g. Graves' disease. 35  Calcitonin hormone : This peptide hormone is synthesized & secreted by Parafollicular cells (c- cells) of the thyroid gland. it is also called ‘’calcium lowering hormone’’ it is not under the control of pituitary or the hypothalamus; It is affected by the level of calcium in the blood. It mobilizes the calcium from blood to the bone & enhances the Osteoblastic activity, so it opposes the Parathyroid hormone. There is increase in its level when there is need to calcium i.e. growth, pregnancy & lactation. 36  Parathyroid gland hormone (PTH) : also called Parathormone Or Parathyrin, is a peptide hormone ; Normally there are 4 parathyroid glands in humans; they are located immediately behind the thyroid gland. It controls the level of calcium &phosphate in the blood by the movement of calcium & phosphate from the bone to blood & excretion of PO4 by the kidney. Usually 99% of calcium is in bone & small fraction is ionized & circulates in blood & this is the active form which performs the physiological action. The level of calcium is 10 mg/dl(9.4 mg/dl) or 5 meq/L in SI units. Calcium present in 3 forms: 1- Non diffusible through capillary membrane form 41%: bound to protein albumin, Globulin. 2- Diffusible through capillary membrane 9% (non ionized). 3-The remaining 50 % of the calcium in plasma is both diffusible & ionized. The phosphate level is 3-4 mg/dl as following distribution : 85% in bone, 14% intracellular, 1% extracellular fluid. 37  Calcium level is controlled by: 1-Parathyroid hormone. 2-Calcitonin.3-vitamine D. Clinical conditions: Hypoparathyroidism (Hypo function of parathyroid Hormone ): This leads to decrease in calcium concentration in the blood → hyperexcitibilty function of the neuromuscular system Hypoparathyroidism may be mild & we have twitching of facial muscles caused by mild stimuli, is called ‘Chvostek' S Sign ‘. The other sign seen is the occlusion of blood flow of the hand like by a sphygmomanometer, so we have flexion of the wrist & thumb, extension of fingers this is called ‘‘Trousseau's Sign’’. 38  2-Hyperparathyroidism: The cause may be: Primary: tumor in the gland (mainly in women because of lactation & pregnancy which predispose for tumors). Secondary: vitamin D deficiency or chronic renal failure. Excessive mobilization of calcium & phosphate from the bone to the extracellular fluid. So If we take x ray to the bone we will see a cyst filled with fibrous tissue so we call this condition ‘’Osteitis Fibrosa Cystica’’. The most important complication is ‘’renal calculi (stones)’’. Other complications: CNS excitability, constipation, weakness & hypophosphatemia. 39  Introduction for Reproductive System ( THE GONADS): The multiple differences between male & female In most species of mammals , depends primarily on: 1- A single chromosome ( chromosome Y ) necessary for the production of testes. 2- Single pair of endocrine structures (Testes in male , Ovaries in female ) After birth, the gonads remain quiescent until adolescence when they are activated by gonadotropins secreted from Anterior pituitary gland ( FSH & LH) hormones. In male , gonadotropins secretion is non cyclic while in post pubertal female there is sequential secretion (serial) necessary for the occurrence of menstruation , pregnancy & lactation. FEMALE HORMONAL SYSTEM: 1. Hypothalamic releasing hormone, called gonadotropin-releasing hormone (GnRH) 2. The anterior pituitary sex hormones, (FSH) & (LH), both are secreted in response to release of GnRH from the hypothalamus 3. The ovarian hormones, estrogen & progesterone, are secreted by the ovaries in response to the two female sex hormones from the anterior pituitary gland. 40  The Ovarian & placental hormones: Estrogens: The naturally occurring estrogens are Estradiol, Estrone, & Estriol. Secretion sites: They are secreted primarily by the ovarian follicles, corpus luteum & placenta. Almost all of this estrogen comes from the ovary & 2 peaks of secretion occur 1- just before ovulation. 2- during the midluteal phase. 41  Effects of Estrogens on Female Genitalia: Their role in the cyclic changes in the endometrium, cervix, & vagina. 1- increases uterine blood flow & increase the amount of uterine muscle & contractile proteins. 2- decreases FSH, while Under some circumstances, inhibits LH (negative feedback); in other circumstances they increases LH secretion by (positive feedback). 3- causes Epiphysial closure in bones ends affecting bone growth in humans. 4- causes salt &water retention. 5- causes a significant plasma cholesterol-lowering Action 6- increases libido ( sex drive force ). 7- controls Female Secondary Sex Characteristics : Estrogens, which are the ―feminizing hormones, responsible for The body changes that develop in girls at puberty, as : A- Enlargement of breasts, uterus, & vagina. 42  B- Bone growth , become thin softer than in men, with wide pelvis & increases the amount of body fat in hips, thighs. C- Voice property & Hair growth. PROGESTERON : Chemistry, Biosynthesis, & Metabolism of Progesterone Progesterone is a steroid secreted by corpus luteum , placenta & follicle in small amounts clearly enter the circulation from the testes & adrenal cortex. About 2% of the circulating progesterone is free , whereas 80% is bound to albumin &18% is bound to corticosteroid-binding globulin Plasma progesterone level : in men is1 nmol /L ; whereas in female is 3 nmol /L during follicular phase &60 nmo /L in luteal phase. 43  Progesterone physiological Actions: The principal target organs of progesterone are uterus, breasts & the brain. 1- It is responsible for progestational changes in endometrium & cyclic changes in cervix & vagina. 2- It has anti estrogenic effect on the myometrial cells. 3- It decreases the number of estrogen receptors in endometrium & increases the rate of conversion of estradiol to less active estrogens. 4- It stimulates development of breast’s lobules ,alveoli & supports secretory function of the breast during lactation. 5- It is thermogenic & is probably responsible for the rise in basal body tempe. at the time of ovulation. Note/ The hormone does not have a significant Anabolic effect 44  Relaxin : is a polypeptide hormone. In female produced in the corpus luteum, uterus, placenta, & mammary glands. Relaxin functions in females : 1- Inhibits uterine contractions during pregnancy, while it relaxes pelvic joints during delivery & softens & dilates uterine cervix. Thus, facilitates delivery. 2- May play a role in the development of mammary glands : Its function in nonpregnant women is unknown. In men, relaxin Produced in the prostate gland in men , found in semen, where it may help to maintain sperm motility & aid in sperm penetration of the ovum. 45  Placental Gonadotropic hormones & Endocrine Changes In all mammals, if fertilization take place , the corpus luteum in ovary at time of fertilization fails to decline & instead enlarges by stimulation of gonadotropic hormones secreted by the placenta. The placental gonadotropin in humans: 1- Human Chorionic Gonadotropin hCG : is a glycoprotein ,It can be measured by radioimmunoassay & detected after conception. Its presence in urine in early pregnancy is basis of various laboratory tests for pregnancy. 2- Human Chorionic Somatomammotropin (hCS ) : This hormone has been called chorionic growth hormone-prolactin (CGP) & human placental lactogen (hPL), but it is now generally called human chorionic somatomammotropin ). 46  MENOPAUSE: At age 40 to 50 years, the sexual cycle usually becomes irregular & ovulation often fails to occur. After a few months to a few years, the cycle ceases totally. Menopause: That period during which cycle ceases & female sex hormones diminish to almost none. The cause of menopause is ‘’burning out ‘’ of the ovaries. At about age 45 years, only few primordial follicles remain to be stimulated by FSH & LH & the production of estrogens by ovaries decreases as number of the primordial follicles reachs zero. The loss of estrogen: often causes marked physiological changes in the function of the body During menopause , including : (1) hot flushes characterized by extreme flushing of the skin, (2) psychic sensations of dyspnea. (3) irritability, (4) fatigue, (5) anxiety, 6) decreased strength & decreased calcification of bones throughout the body. 47  The Male Reproductive System Hormonal control of spermatogenesis: The maturation from spermatids to spermatozoa depends on androgen acting on the Sertoli cells in which the developing spermatozoa are inserted. FSH acts on the Sertoli cells to facilitate the last stages of spermatid maturation. Also, it promotes production of Androgen Binding Protein ( ABP). 48  Endocrine Function Of The Testes: Chemistry & Biosynthesis of ’’ Testosterone’’: Testosterone, the principal hormone of the testes, It is synthesized from cholesterol in the Leydig cells & is also formed from Androstenedione secreted by the adrenal cortex. The biosynthetic pathways: 1- Direct pathway : In Leydig cells 2- Indirect pathway in Adrenal gland : Dehydroepiandrosterone (DHEA) & Androstenedione. are then converted to testosterone. The secretion of testosterone is under the control of LH as LH stimulates Leydig cells.. Testosterone Physiological Actions 1- Acts during development of internal genitalia ; ( Testosterone–receptor complexes ) are responsible for maturation & formation of male internal genitalia. 2- Testosterone & other androgens do an inhibitory negative feedback effect on pituitary LH. 3- Development & maintenance of male secondary sex characteristics; by apply an important protein-anabolic, growth-promoting effect. 4- maintains spermatogenesis, along with FSH. 49  Dihydrotestosterone (DHT) Physiological Action: 1- DHT–receptor complexes are needed to form male external genitalia organs. 2- Facial hair Growth , development of the acne. Note :The increase in muscle mass & the development of male sex drive & libido depend primarily on testosterone rather than DHT. Control of Testicular Function: FSH is tropic for Sertoli cells : FSH & androgens maintain Gametogenic function of testes. FSH stimulates secretion of ABP (androgen binding protein) & Inhibin. Inhibin feeds back to inhibit FSH secretion. LH is tropic for Leydig cells & stimulates secretion of testosterone, which in turn feeds back to inhibit LH secretion. Note :Hypothalamic lesions in animals & humans lead to atrophy of the testes & loss of their function. 50  Inhibins: is a peptide hormone secreted by the Sertoli cells in men and by the granulosa cells in women. There are 2 inhibins types A & B : A. from testes ,Inhibins are produced by Sertoli cells that inhibits FSH secretion. B. from ovarian follicles Granulosa cells in females. Note/ Both (inhibin A) & (inhibin B) inhibit FSH secretion by a direct action on the pituitary, though it now appears that it is inhibin B is the FSH-regulating inhibin. 51