Kidney Physiology Overview

Kidney Physiology

• Study of kidney function, including its role in homeostasis, endocrine functions, nephron structures, and common disorders.

Objectives

• Students will be able to describe kidney functions.
• Students will be able to list the endocrine functions of the kidney.
• Students will be able to describe basic nephron functions.
• Students will be able to outline calcium and phosphate homeostasis.
• Students will be able to describe manifestations of kidney disorders.

Kidney Functions

• Sodium balance: Regulates extracellular fluid volume and blood pressure.
• Plasma osmolality: Maintains the concentration of dissolved substances in the blood.
• Potassium balance: Keeps potassium levels in the blood stable.
• Calcium balance: Maintains calcium levels in the blood.
• Phosphorous balance: Maintains phosphorous levels in the blood.
• Glucose balance: Regulates glucose levels in the blood.
• Acid-base balance: Regulates the balance of acids and bases in the blood.
• Arterial O2 detection and content: Detecting and controlling the level of oxygen in the blood.
• Nitrogenous waste removal: Eliminates waste products, like urea and creatinine.

Kidney Macrostructure

• The kidney is composed of cortex and medulla
• Has renal artery, renal vein, renal hilum, minor calyx, major calyx, renal pelvis, pyramid, papilla, and renal column.

Nephron Structure

• The functional unit of the kidney is the nephron.
• Millions of nephrons are found in each kidney.
• Components include afferent arteriole, glomerulus, Bowman's capsule, proximal convoluted tubule, Henle's loop, distal convoluted tubule, and collecting duct.
• The nephron is essential for filtration, reabsorption and secretion.

Microscopic Images of the Kidney

• Glomerulus: Shows capillaries and important for filtration.
• Tubules: Shows the proximal and distal convoluted tubules.
• Proximal tubule cells: Contain microvilli, important for reabsorption.

Vascular Supply of the Kidney

• Kidneys receive 25% of cardiac output.
• Venous oxygen saturation is approximately 90%.
• Blood vessels include afferent and efferent arterioles, cortical-radial arteries, arcuate arteries, and interlobar arteries.

Basic Functions of the Nephron

• Filtration: Filtering of blood in the glomerulus.
• Reabsorption: Recovering of necessary substances from the filtrate.
• Secretion: Removing of waste products from the blood into the filtrate.
• Excretion: Removal of waste products via urine.

Processes Occurring in the Nephrons

• About 20% of the plasma is filtered in the glomerulus.
• Proteins are not filtered due to their size.
• Normal capillaries surrounding the tubules are in the peripheral region.

Water and Substances Handling by the Kidney

• Glomerular Filtration Rate (GFR) is ~125 mL/min (~180 L/day).
• About 1% of the filtrate is excreted in urine.
• About 99% of plasma entering the kidney returns to the systemic circulation.
• 20% of the volume filters, but 19% of fluid is reabsorbed.
• About 99.9% of water is reabsorbed in the tubules.
• About <1% volume is excreted.

Kidney and Vitamin D3

• Vitamin D3 is activated in the kidney by the enzyme 1α-hydroxylase.
• The production of 1,25(OH)2D3 plays a major role in the endocrine function of the kidney.

Kidney Disease

• Diabetic Nephropathy: A disease that often affects people with diabetes.
• Polycystic Kidney Disease: A genetic disorder causing numerous cysts in the kidneys.

Endocrine Functions of the Kidney

• Calcitriol: Activating vitamin D, essential for calcium and phosphate homeostasis.
• Erythropoietin: Important for red blood cell (RBC) stimulation.

Kidney Physiology Summary

• The kidney is responsible for several vital homeostatic functions while excreting waste products and maintaining fluid and electrolyte balance.
• The nephron is the functional unit performing crucial processes like filtration, reabsorption, and secretion.
• The processes involved are complex and carefully regulated by various hormones and systems to maintain water and electrolyte homeostasis, including calcium and phosphorus levels.
• Specific disorders can affect kidney function, resulting in various symptoms and the necessity of interventions like dialysis for severe cases.

Endocrine System

• Composed of glands secreting hormones regulating various bodily functions.
• Primarily includes hypothalamus, pituitary gland, thyroid, parathyroid, adrenal glands, pancreas, ovaries (females), testes (males), and the pineal gland.

Basic Information about the Endocrine System

• Hormones are chemical messengers influencing metabolism, tissue functions, growth & development, sexual function, reproduction, sleep, and mood.
• The word "endocrine" originates from Greek words "endo" meaning "within" and "crinis" meaning "to secrete."

Basic elements of the Endocrine System

• Hypothalamo-pituitary complex
• The thyroid
• Endocrine pancreas
• Calcium homeostasis
• Adrenal system
• Growth hormone axis
• Reproductive axis

Hypothalamus & Pituitary

• The hypothalamus regulates satiety, metabolism & body temperature; secretes hormones affecting pituitary gland function.
• The pituitary gland is the master gland and is connected to the hypothalamus. Its anterior lobe releases several critical hormones for growth and function of various other glands.
• Posterior lobe secretes hormones crucial for regulating water balance.
• Hypothalamic and pituitary hormones together help regulate body functions such as growth, water balance, reproduction, and stress responses.

Thyroid Gland

• Located in the neck.
• Produces thyroid hormones regulating metabolism, blood pressure, heart rate, bone growth, digestion, muscle tone, reproduction, and nervous system development in children.

Endocrine Pancreas

• Secretes insulin and glucagon regulating glucose levels in the blood.

Reproductive Glands

• Testes (males): Secrete androgens affecting many male characteristics (sexual development, facial & pubic hair growth, sperm production).
• Ovaries (females): Produce estrogen and progesterone controlling female characteristics and reproductive functions.

Adrenal Glands

• Located on top of each kidney.
• Adrenal cortex produces corticosteroids regulating metabolism, salt & water balance, the immune system and sexual function.
• Adrenal medulla produces catecholamines helping the body cope with stress (increasing heart rate & blood pressure).

Parathyroid Glands

• Located on the surface of the thyroid.
• Release parathyroid hormone regulating calcium levels in blood and bone metabolism.

Common Endocrine Disorders

• Various diseases impacting endocrine function, such as diabetes mellitus, thyroid disease, prolactinoma, acromegaly, Cushing's disease, and congenital adrenal hyperplasia (CAH), exhibiting different incidences (frequency).

Growth Hormone Abnormality

• Acromegaly - excess growth hormone after epiphyseal closure.
• Gigantism - excess growth hormone before epiphyseal closure.
• Dwarfism - growth hormone deficiency in children leading to short stature.

Thyroid Disorders

• Hyperthyroidism - excessive thyroid hormone production.
• Hypothyroidism - insufficient thyroid hormone production.

References

• Guyton & Hall Textbook of Medical Physiology
• Lippincott Illustrated Reviews Physiology