Hormonal Regulation of Renal Function | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Antidiuretic Hormone (ADH) and Water Conservation

• ADH Function:
  • ADH is a hormone regulating water conservation in the body.
  • Produced in the hypothalamus and stored in the posterior pituitary gland.
• Collecting Duct Permeability:
  • ADH determines the permeability of the collecting duct to water.
  • Monitors the ratio of water to solutes in the blood.
• Release of ADH:
  • Hypothalamus releases more ADH when water content is low compared to solutes.
  • Makes the collecting duct more permeable to water.
• Aldosterone and ADH Interaction:
  • Presence of both aldosterone and ADH draws more water out of the collecting duct.
  • Distal tubule actively pumps out ions, leading to water movement by osmosis.
• Effect on Urine:
  • Result is concentrated urine with less volume.
• ADH Release Factors:
  • Low blood pressure triggers more ADH release.
  • Special receptors in the heart's left auricle monitor blood pressure.
• External Factors:
  • Drugs like alcohol and caffeine suppress ADH release.
  • This suppression can lead to dehydration.

Adenohypophyseal Hormone

Growth Hormone (Somatotropin):

• Adenohypophyseal hormones also impact renal function.
• Growth hormone has a tropic effect on the kidneys.
• Increases Glomerular Filtration Rate (GFR) and Effective Renal Plasma Flow (ERPF).

Hormonal Regulation of Renal Function

• Thyroid Stimulating Hormone (TSH):
  • Indirectly influences growth hormone through thyroid hormones (triiodothyronine and thyroxine).
  • Mediates changes in renal function.
• ACTH (Adrenocorticotropic Hormone):
  • Directly affects renal function through steroid hormones from the adrenal cortex.
• Adrenal Cortex: Aldosterone:
  • Loss of sodium chloride and water in urine.
  • Retention of potassium and urea in plasma during adrenal insufficiency.
• Aldosterone:
  • Primary mediator of renal sodium and potassium regulation.
  • Directly impacts tubular function, allowing normal sodium reabsorption and potassium excretion.
  • Sympathetic stimulation increases renin secretion, affecting aldosterone levels.
• Renin-Angiotensin System:
  • Juxtaglomerular cells release renin.
  • Renin-angiotensin system stimulates aldosterone secretion.
• Cortisol and Water Excretion:
  • Similar effects to aldosterone on renal sodium and potassium regulation.
  • Mobilizes water for excretion or translocation among body water compartments.
• Parathyroid Hormone (PTH):
  • Regulates calcium and phosphate excretion in urine.
  • Influences phosphate reabsorption and hydroxylation of active Vitamin D.
• Prostaglandins:
  • Certain medullary components produce vasodepressor prostaglandins.
  • Prostaglandins of the E-series are natriuretic, increasing urinary sodium excretion.
• Reflexes Influencing Renal Function:
  • Sympathetic efferent pathway alters blood flow within the kidney.
  • Activation during decreased blood pressure redistributes blood flow, affecting sodium balance.

Renal Responses to pH and Electrolyte Changes

Metabolic Acidosis:

• Results from excess hydrogen ion production.
• Compensated by reducing total plasma carbon dioxide content.
• Henderson-Hasselbalch equation maintains pH equilibrium.

Acid-Base Balance in the Body

Metabolic Acidosis

• Occurs when the loss of bicarbonate exceeds the loss of carbon dioxide.
• Kidneys respond by increasing hydrogen ion secretion into urine and enhancing bicarbonate reabsorption.
• Increased hydrogen ion secretion helps conserve fixed cations.
• Formation of certain compounds (acetoacetates, B-hydroxy butyrates) in metabolic acidosis may lead to sodium and potassium excretion in urine.
• In uncompensated cases, sodium loss into urine can be significant, potentially causing hypokalemia.

Respiratory Acidosis

• Results from the retention of carbon dioxide in the body.
• Kidneys compensate by increasing hydrogen ion secretion and returning bicarbonate to extracellular fluid.
• Compensatory mechanism is usually insufficient to fully restore pH to normal levels.
• The increased plasma pCO₂ tends to raise bicarbonate levels, aiding in bicarbonate reabsorption.

Respiratory Alkalosis

• Caused by hyperventilation, leading to a primary deficit of carbon dioxide.
• Kidneys respond by decreasing bicarbonate reabsorption due to decreased pCO₂ in arterial blood.
• Both respiratory carbon dioxide loss and increased renal bicarbonate excretion reduce the total bicarbonate buffer capacity.
• This may contribute to the development of a secondary metabolic acidosis.

Endocrine Gland Regulation

Pancreas and Parathyroids

• Similar to spinal reflex in the nervous system.
• Sensitive to concentrations of specific chemicals.
• Not isolated; influenced by other endocrine glands.
• Example: Afferent neural pathway activates adrenal medulla, increasing blood glucose, leading to insulin secretion from pancreatic islets.

Tropic Hormones and Target Glands

• Pituitary tropic hormones regulate other endocrine glands.
• Secretions from target glands serve as feedback controls for pituitary hormones.
• Circulating hormones may influence higher CNS centers, impacting tropic hormone secretion.

Prostaglandins

• Unique means of endocrine control.
• Secreted in response to various stimuli.
• Have powerful systemic effects.

Anti-Hormones

• Antibodies against insulin, parathormone, calcitonin, glucagon, and six anterior pituitary hormones have been produced and studied.

Pituitary Gland and Hypothalamus

• Intimately related morphologically and functionally.
• Hormones of the adenohypophysis (anterior pituitary): FSH, LH, Prolactin, ACTH, TSH, Growth Hormone.
• Role in reproduction:
  • FSH and LH collectively known as gonadotropins.
  • FSH acts on ovarian follicles in females, promoting maturation and overall follicular growth.
  • In males, FSH stimulates Sertoli cells for spermatogenesis.
  • LH intensifies growth, initiates estrogen secretion, and promotes ovulation in females.
  • In males, LH stimulates testosterone secretion.
  • Prolactin in females is necessary for mammary growth and lactation initiation and maintenance.
  • Prolactin function in males not fully understood.

Adrenocorticotropic Hormone (ACTH)

• Released by the anterior pituitary under hypothalamic stimulation.
• Corticotropin Releasing Hormone from hypothalamus triggers ACTH synthesis and release.
• Stress stimulates corticotropin releasing hormone, while cortisol may inhibit its release.
• Vasopressin also stimulates ACTH synthesis.
• ACTH regulates water balance and stimulates adrenal cortex to produce glucocorticoids.
• Short half-life (less than 10 minutes).
• Effects include increased adrenal blood flow, mobilization of fatty acids, enhanced ketogenesis, increased muscle glycogen, hypoglycemia, and decreased plasma amino acids.
• Stimulates aldosterone production.

Thyroid Stimulating Hormone (TSH)

• Released by the anterior pituitary.
• Acts on the thyroid gland.
• Increases alveolar epithelium height and stimulates colloid endocytosis for hormone release.

Growth Hormone

• Stimulates body size increase through protein synthesis and metabolic mass enhancement.

Intermedin (Melanophore Stimulating Hormone - MSH)

• Causes color changes in reptiles, amphibians, and fish in response to light, temperature, or humidity.
• Regulation of adenohypophyseal secretion involves both hormonal and neural influences.

Pineal Gland (Epiphysis Cerebri)

• Pineal tumors in children may delay sexual development.

Thyroid Gland

• Thyroxine hormone contains iodine.
• Effects can be morphological and functional.
• Morphological changes include feather regeneration, skin, and hair effects.
• Thyroid deficiency in lambs can impact the quality of the adult fleece.

Thyroid Hormones and Effects

• Major Outcomes of Hypothyroidism:
  • Abortion, stillbirth, and weak live births.
  • Delayed puberty, irregular estrous cycles, and reduced fertility in females.
  • Decreased testicular growth, impaired spermatogenesis, and lowered libido in males.
  • Seasonal reduction in semen quality in rams.
• Impact on Mammary Gland:
  • Thyroxine is a potent galactopoietic agent.
  • Thyromimetic substances increase milk production.
  • Example: Iodinated casein with crystalline thyroxine.
• Functional Effects:
  • Increases oxygen consumption rate and internal heat production.
  • Enhances cellular glucose absorption and glycogenolysis.
  • Thyroid deficiency leads to increased serum cholesterol and obesity.
  • Important for fat deposition in livestock for meat quality and weight gain efficiency.
• Goitre and Causes:
  • Enlarged thyroid gland associated with hyper or hypothyroidism.
  • Iodine deficiency and certain foods like cabbage inhibit thyroid activity.
• Anti-Thyroid Substances:
  • Thiocarbamides, thiourea, and thiouracil inhibit iodine conversion or binding.
  • Other drugs like sulphonamides, p-aminosalicylic acid, amphenone, phenylbutazone, and chlorpromazine.

Hormones for Calcium and Bone Regulation

Parathyroid Gland and Parathormone (PTH):

• PTH mobilizes calcium from bones.
• Increases phosphate excretion and enhances renal retention of calcium.
• Maintains calcium environment and regulates bone remodeling.

Parathyroid Gland and Hormones

• Rubber Jaw Syndrome in Dogs:
  • Prolonged activation of parathyroid leads to skeletal demineralization.
  • In dogs, it manifests as "Rubber Jaw Syndrome," making the jaw pliable and rubber-like.
• Calcitonin:
  • Produced by Pars follicular cells outside thyroid follicles.
  • Secreted in response to high blood calcium levels.
  • Opposes parathormone by inhibiting bone resorption.
• 1-2, 5 Dihydroxycholecalciferol:
  • Regulates bone and mineral balance.
  • Increases calcium absorption in intestines and retention in kidneys.
  • Aids bone formation by enhancing maturation of bone matrix.
  • Interacts with PTH (Parathyroid Hormone).

Pancreas and Hormones

• Insulin and Glucagon:
  • Secreted by pancreatic islets of Langerhans.
  • Insulin deficiency leads to glycosuria, elevated blood sugar, polyphagia, polydipsia, polyuria, ketonemia, hypercholesterolemia, negative nitrogen balance, emaciation, dehydration, and death.
  • Without insulin, glucose utilization is depressed, forcing fat mobilization for energy, leading to ketone body formation.
  • Decreased glucose utilization increases gluconeogenesis and protein catabolism, causing potassium diuresis and enzyme defects.
  • Insulin regulates glucose transport into cells through a carrier system.
• Function of Glucagon:
  • Prevents fat storage.

Adrenal Gland

Two Functional Parts: Adrenal Cortex and Adrenal Medulla.

Adrenal Medulla and Hormones

• Amines from Tyrosine:
  • Norepinephrine and Epinephrine are derived from tyrosine.
  • Both stimulate α- and β-receptors, with norepinephrine being more potent in some cases.
• Effects on Blood Vessels:
  • Epinephrine in moderate doses decreases peripheral resistance due to β receptors, causing skeletal muscle dilation.
  • Norepinephrine increases peripheral resistance as a general vasoconstrictor.
• Effects on Heart:
  • Catecholamines accelerate depolarization and enhance transmission in cardiac muscle, increasing heart rate and contraction force.
  • Norepinephrine increases systolic, diastolic, and mean blood pressures.
• Respiratory and Metabolic Effects:
  • Both amines dilate bronchi and increase respiration rate.
  • Metabolic effects include hyperglycemia, calorigenesis, lipolysis, elevated blood lactate, and increased serum potassium.
• Smooth Muscle Effects:
  • Relaxation of ciliary, bronchial, esophageal, stomach, and bladder detrusor muscles through β-receptors.
  • Constriction of smooth muscles in the eye, stomach pylorus, intestinal sphincter, and bladder trigone and sphincter through α-effects.

Other Pressor Substances

• Kinins, Angiotensin, Substance P, and Lipid Anions:
  • Physiologically active substances influencing blood pressure and other processes.
• Adrenocortical Hormones:
  • Derivatives of 21-carbon pregnane nuclei.
  • Seven recognized corticosteroids, with aldosterone being unique due to an aldehyde in place of a methyl group at C13.

Salt Balance and Aldosterone

• Aldosterone Secretion:
  • Zona glomerulosa of the adrenal cortex secretes aldosterone.
  • Aldosterone influences salt balance and has glucocorticoid activity.
• Synthesis Regulation:
  • Aldosterone synthesis increases with high potassium (K) or significant decrease in sodium (Na) levels.
• Catabolism of Steroid Hormones:
  • Steroid hormones are broken down and inactivated mainly in the liver, kidneys, and target organs.

Glucocorticoids

• Carbohydrate Metabolism:
  • Glucocorticoids primarily affect carbohydrate metabolism, enhancing gluconeogenesis.
• Effects on Immune System:
  • Cause lymphoid tissue breakdown, leading to lymphopenia and eosinopenia.
  • Enhance water retention.
• Anti-inflammatory Effects:
  • Used to treat inflammation by reducing hyperemia, cellular response, exudation, and fibroblast formation.
  • Diminish allergic responses.

Adrenal Sex Hormones

• Non-Gonadal Secretion:
  • Adrenal cortex produces weak androgen steroids.
  • Sex hormones, traditionally linked to ovaries and testes, are also secreted by non-gonadal sources.
• Classifications:
  • Androgens (e.g., testosterone)
  • Estrogens (e.g., estradiol)
  • Progestins (e.g., progesterone)
  • Relaxin
• Key Hormones:
  • Testosterone is a potent androgenic steroid.
  • Estradiol is a major ovarian estrogen in cows.
  • Progesterone is a key sex hormone with progestational activity.

Testosterone

Source: Produced by interstitial cells of the testis.

Oestrogens and Progestins

Sources

• Theca interna cells secrete oestrogens.
• Granulosa cells secrete progesterone and other progestins.
• Placenta, especially in pregnant animals, is a significant source of progestins and oestrogens.

Placental Production

• Placenta contributes to progestin and oestrogen secretion during pregnancy in various species.

Relaxin

Source:

• Found in placentas during pregnancy, mainly produced by ovaries in animals.

Estrogen Actions

• Female Genital Passage:
  • Prepare female genital passage for copulation.
  • Essential for a successful union between male and female gametes.
• Uterine Effects:
  • Induce growth in the uterus.
  • Influence motility and contractility of the female reproductive tract.
• Oviductal Effects:
  • Synergistic actions with progesterone on oviductal cilia.
  • Estrogen promotes ciliogenesis, while progesterone enhances cilia beats.

Progestin Actions

Implantation and Pregnancy: Necessary for implantation and maintenance of pregnancy.

Mating Behavior

Influence on Female Mating Behavior:

• Effects on mating behavior vary among animals.
• In cows, induces short-term behavioral estrus.
• In hens, prolactin secretion causes broodiness.

Pregnancy Maintenance

Role of Progestins:

• Essential for maintaining pregnancy.

Mammary Development and Lactation

Control and Influence:

• Various hormones influence mammary development and lactation.
• Ovarian sex steroids and prolactin play crucial roles in mammary growth.
• Estrogen rises at the end of pregnancy, stimulating prolactin, initiating and sustaining lactation through the interaction of suckling and pituitary prolactin secretion.

Relaxin

• Production:
  • Produced by the corpus luteum in late pregnancy.
• Functions:
  • Induces relaxation of sacrococcygeal joints, widening the birth canal.
  • Causes cervical dilatation.
  • Results in decalcification of the pelvic girdle, facilitating birth canal relaxation.

Placental Gonadotrophins

• Serum Gonadotrophin (PMSG):
  • Similar to chorionic gonadotrophins.
  • Active in promoting follicular growth, resembling FSH.
  • Obtained from the serum of pregnant mares.
• Chorionic Gonadotrophins (HCG):
  • Resembles anterior pituitary hormones.
  • Formed in the placenta and excreted in the urine of pregnant women.
  • Primarily luteinizing in action, with little effect on follicular growth.

Prostaglandins (PG)

• PGF2α:
  • Potent in terminating early pregnancy.
  • Acts through vasoconstriction of utero-ovarian veins or by stimulating uterine contraction.
  • Used in veterinary medicine for estrous synchronization.
• Circulatory Effects:
  • Vary among prostaglandin compounds and species.
  • PGE1 and PGE2 are peripheral vasodilators.
  • PGF2α acts as a vasopressor.
• Other Actions:
  • Inhibition of gastric secretion.
  • Relaxation of bronchial musculature.
  • Enhancement of inflammation.
  • Inhibition of sympathetic neuroeffector transmission.

Thymus Gland

Importance

• Essential for normal development and maintenance of immunological competence.
• Plays a crucial role in the immune system.