Urinary System Anatomy and Functions

The urinary system regulates plasma ion balance, volume, osmolarity, and pH; removes waste products; secretes erythropoietin and renin; activates Vitamin D3; and performs gluconeogenesis.

The kidneys are bean-shaped, roughly the size of a fist, and weigh approximately 115-170 grams.

Paired kidneys are located behind the abdominal lining (retroperitoneal).

Urine is formed in the kidneys, travels through the ureters to the bladder, and is excreted through the urethra.

Kidneys, ureters, bladder, and urethra, work together to filter blood, collect waste (urine), and excrete it.

The process where blood is filtered from the glomerulus into Bowman's capsule.

The process where useful substances are reabsorbed from the tubules back into the peritubular capillaries.

The process where waste products are secreted from the peritubular capillaries into the tubules.

The process where waste products are excreted from the tubules out of the body.

It carries blood to the glomerulus for filtration.

It carries filtered blood away from the glomerulus.

They surround the proximal and distal tubules, enabling reabsorption and secretion.

It helps regulate blood pressure and filtration rate by secreting renin.

The volume of fluid filtered from the glomerular capillaries into Bowman's capsule per unit time. It reflects the overall efficiency of kidney filtration.

A mechanism where the smooth muscle in afferent arterioles contracts in response to increased stretch caused by higher blood pressure, thus constricting the arterioles and reducing GFR.

A mechanism where the macula densa cells in the distal tubule sense changes in flow rate and sodium concentration and release paracrine signals to regulate afferent arteriole diameter and GFR.

Decreased blood pressure directly reduces filtration pressure, leading to a lower GFR. Additionally, extrinsic controls can further decrease GFR to maintain blood pressure.

External factors like hormones and the nervous system regulate GFR to maintain blood pressure and volume. For example, decreased blood pressure triggers the release of hormones to constrict arterioles and increase GFR.

Three layers must be passed for filtrate to enter Bowman's capsule: the capillary endothelial layer, the basement membrane, and the surrounding epithelial layer (podocytes).

Physical forces that govern the movement of fluid across capillary walls, including hydrostatic pressure (pushing force) and oncotic pressure (pulling force).

The forces that promote the movement of fluid from the glomerular capillaries into Bowman's capsule due to the high hydrostatic pressure in the capillaries and low oncotic pressure in Bowman's capsule.

The forces that resist the movement of fluid from the glomerular capillaries into Bowman's capsule. These include hydrostatic pressure within Bowman's capsule and oncotic pressure within the glomerular capillaries.

The pressure of fluid within a vessel or space, pushing fluid out.

The pressure created by the presence of proteins in a fluid, pulling water towards it.

The movement of substances from the renal tubules back into the bloodstream.

Most reabsorption happens in the proximal tubules, the first part of the nephron.

The movement of dissolved substances like glucose, salts, and amino acids from the tubules back into the blood.

Some solute reabsorption also occurs in the distal convoluted tubules.

Epithelial cells lining the renal tubules and endothelial cells of capillaries. The capillaries are the smallest blood vessels.

The body responds by increasing blood pressure through mechanisms like vasoconstriction and increasing heart rate.

By constricting blood vessels (vasoconstriction), increasing heart rate, and increasing fluid retention by the kidneys.

When blood pressure rises, mechanisms are activated to lower it; when blood pressure falls, mechanisms are activated to raise it.

The fluid-filled area surrounding the renal tubule cells. It is a continuation of the interstitial fluid surrounding the kidneys.

The interior space within a hollow structure, like the renal tubule. It contains filtrate, which is the fluid that is filtered from the blood.

The cell membrane facing the lumen of the renal tubule.

The cell membrane facing the interstitial fluid and peritubular capillaries.

The maximum rate at which a substance can be transported across a membrane by carrier proteins.

The concentration of a substance in the plasma above which it begins to appear in the urine.

Carrier proteins actively transport glucose across the apical membrane of the proximal tubule cells using secondary active transport. They then facilitate diffusion of glucose across the basolateral membrane.