Human Anatomy: Kidney Functions and Structure

The ureter is a tube that carries urine from each kidney to the urinary bladder.

The adrenal glands are located on top of each kidney, playing a crucial role in hormone production.

The kidneys are positioned behind the peritoneum and surrounded by fat and connective tissue, offering them protection.

The renal fascia is a strong layer of connective tissue that anchors the kidneys to the abdominal wall, ensuring they stay in place.

The renal artery carries oxygenated blood to the kidneys, and the renal vein carries deoxygenated blood away.

The renal capsule is a protective layer of connective tissue that surrounds each kidney.

The hilum is the point on the kidney where the renal artery, nerves, and veins enter and exit.

Transitional epithelium, found in the ureters and urinary bladder, changes shape from cuboidal (relaxed) to squamous (stretched) to accommodate varying urine volumes.

The smooth muscle lining the ureters and bladder contracts involuntarily to propel urine from the kidneys to the bladder and then out through the urethra.

The internal urethral sphincter, composed of smooth muscle, is located at the junction of the bladder and urethra. It prevents involuntary urine leakage.

An additional, voluntary muscle called the external urethral sphincter provides conscious control over urination.

During ejaculation in males, the internal urethral sphincter contracts, preventing semen from entering the bladder and ensuring it exits through the urethra.

Filtration in the kidneys is a nonselective process that separates substances based on size or charge. It's like a sieve that lets small particles through. However, it doesn't get rid of everything in the blood.

Reabsorption in the kidneys involves moving substances from the filtered urine back into the bloodstream.

Secretion in the kidneys involves removing substances from blood and adding them to the urine.

The kidneys play a crucial role in maintaining water balance, regulating blood pressure, and filtering waste products from the blood.

Most of the water and essential substances in the filtrate are reabsorbed back into the bloodstream, preventing dehydration and deficiency.

The process where substances leave the filtrate and enter the peritubular capillaries, ultimately returning to the bloodstream.

The descending limb of the loop of Henle is highly permeable to water, allowing water to move out by osmosis.

The ascending limb of the loop of Henle is impermeable to water, but permeable to solutes.

The thick segment of the ascending limb actively reabsorbs sodium chloride, contributing to the concentration gradient in the medulla.

The process of filtration in the kidneys removes waste products and excess water from the blood, forming filtrate.

The process of removing substances from the filtrate as it passes through the renal tubules.

A specialized network of blood vessels that surround the renal tubules, facilitating reabsorption of substances.

The pressure difference between the filtrate inside the tubule and the blood in the peritubular capillaries, driving reabsorption.

The volume of the filtrate is reduced by approximately 65% by the time it reaches the end of the proximal convoluted tubule.

The medullary concentration gradient is the difference in solute concentration between the renal medulla and the cortex. This gradient is crucial for concentrating urine and conserving water. It also plays a role in maintaining blood pressure.

Urea recycling is a process where urea, a waste product from protein breakdown, is reabsorbed and secreted multiple times in the kidneys. This recycling amplifies the medullary concentration gradient by further increasing the solute concentration in the medulla.

The renin-angiotensin-aldosterone system is triggered by low blood pressure. Renin released from the kidneys converts angiotensinogen to angiotensin I, which is further converted to angiotensin II. Angiotensin II raises blood pressure, increases thirst, and stimulates aldosterone secretion.

Antidiuretic hormone (ADH), also known as vasopressin, is released by the pituitary gland in response to dehydration. ADH acts on the kidneys to increase water reabsorption, making urine more concentrated.

Atrial natriuretic hormone (ANH), released from the heart, opposes the effects of aldosterone by promoting sodium excretion and water loss. It helps decrease blood volume and blood pressure.

Simple cuboidal epithelium lining the thick segment of the nephron, actively transporting solutes using ATP-powered pumps and carrier molecules, contributing to water conservation by the kidneys.

The movement of substances from the blood into the filtrate, often involving toxic byproducts of metabolism, drugs, or molecules not normally produced by the body.

The active transport of sodium ions (Na+) across the membrane followed by passive transport of potassium ions (K+) and chloride ions (Cl-) along with water.

The ability of the kidneys to regulate urine volume and concentration, primarily dependent on countercurrent mechanisms, hormones, and the permeability of the nephron segments.

A countercurrent mechanism involving fluid flowing in opposite directions in adjacent structures, allowing for exchange of materials between them.

Hormone that promotes water reabsorption in the distal convoluted tubule and collecting duct, influencing urine concentration.

The renin-angiotensin-aldosterone system (RAA) regulates blood pressure and electrolyte balance by promoting sodium reabsorption and potassium excretion.

Atrial natriuretic hormone (ANH) promotes sodium excretion and inhibits aldosterone release, contributing to blood pressure reduction.

The movement of substances from the blood into the filtrate, often involving toxic byproducts of metabolism and drugs or molecules not normally produced by the body.

Ammonia, a toxic by-product of protein metabolism, is secreted by the epithelial cells of the renal tubule.