Chapter 24 Urinary System

micturition

urination

glomerular filtration

The first step in urine formation in which substances in blood pass through the filtration membrane and the filtrate enters the glomerular (Bowman's) capsule and then travels into the proximal convoluted tubule of the nephron.

Glomerular Filtration Rate (GFR)

the amount of filtrate formed per minute by the two kidneys combined

ureter

tube that carries urine from the kidney to the urinary bladder

urethra

tube that carries urine from the bladder to the outside of the body

nephron

functional unit of the kidney

urinary bladder

hollow, muscular sac that holds and stores urine

fibrous capsule of kidney

-Dense, irregular connective tissue covering the entire outer surface of the kidney
-Maintains shape of kidney
-Protects kidney from damage
-Prevents infection from spreading

perinephric fat

thick layer of adipose tissue between the inner fibrous capsule of the kidney and the renal fascia that anchors the kidney to surrounding structures.

renal fascia

outer layer of dense fibrous connective tissue that anchors the kidney to surrounding structures

retroperitoneal

located behind the peritoneum

renal hilum

area in the midportion of the kidney where the renal vessels and ureter enter and exit

renal pelvis

funnel-shaped reservoir that collects the urine and passes it to the ureter

minor calyx of the kidney

extension of the pelvis, form cup-shaped areas that enclose the tips of the renal pyramids

renal pyramids

triangular-shaped areas of tissue in the medulla of the kidney

renal medulla

inner portion of the kidney

renal cortex

outer portion of the kidney

renal column

Inward extensions of the cortex tissue separating the renal pyramids.

major calyx of the kidney

The cavity formed by the convergence of several minor calyces, which drain urine from the minor calyxes into the renal pelvis

renal artery

blood vessel that carries oxygenated blood to the kidney

afferent arteriole

The small artery that carries blood toward the capillaries of the glomerulus.

efferent arteriole

The small artery that carries blood away from the capillaries of the glomerulus.

glomerulus

A network of capillaries surrounded by glomerular (Bowman's) capsule in the nephron and serving as the site of filtration in the vertebrate kidney.

renal corpuscle

glomerulus and glomerular (Bowman's) capsule

renal vein

blood vessel that carries deoxygenated blood away from the kidney and toward the heart

peritubular capillaries

The network of tiny blood vessels that surrounds the proximal and distal tubules in the kidney. These tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron

vasa recta

The capillaries that surround the loop of Henle of the nephron. The vasa recta reclaims reabsorbed substances, such as water and sodium ions.

podocytes

Cells in the Bowman's capsule in the kidneys that wrap around capillaries of the glomerulus. These cells have branching tentacle-shaped extensions (pedicles) that help constitute the barrier through which blood is filtered in the glomerulus of the kidney.

filtration slits

formed by pedicels of podocytes; substances filter between the pedicels based on size

fenestrated capillaries

have pores in vessel wall; found in kidneys, intestines, and endocrine glands

intraglomerular mesangial cells

Specialized cells derived from smooth muscle. Their contraction decreases luminal diameter of glomerular capillaries and decreases filtration slit size. They will contract in response to GFR that is too high. By contracting, they effectively lower GFR.
They are also capable of phagocytosing debris.

macula densa

The cells of the distal tubule at the juxtaglomerular apparatus. They are receptors that monitor filtrate osmolarity as a means of regulating filtration rate. If a drop is osmolarity is sensed, the macula densa dilates the afferent arteriole (to increase the blood pressure in the glomerulus and thus increase filtration) and stimulates the juxtaglomerular cells to secrete renin (to raise systemic blood pressure).

extraglomerular mesangial cells

Located between arteriole and tubule cells
Interconnected with gap junctions
May pass signals between macula densa and granular cells. Exact function unclear.

juxtaglomerular cells

specialized smooth muscle cells in wall of afferent arteriole. They are baroreceptors that secrete renin upon sensing a decrease in blood pressure. Also capable of secreting EPO in response to low blood volume.

juxtaglomerular apparatus

in the nephron, the complex of cells (macula densa, extraglomerular mesangial and juxtaglomerular cells) from the distal tubule and the afferent arteriole which helps regulate blood pressure by secreting renin and EPO as well as vasodilating the afferent arteriole in response to low blood pressure; located near the glomerulus

cortical nephrons

-85% of all nephrons; almost entirely in cortex
- have short nephron loops
- have efferent arterioles that branch into peritubular capillaries around PCT and DCT

juxtamedullary nephrons

nephrons with well-developed loops of Henle that extend deeply into the renal medulla

urea

A chemical that comes from the breakdown of proteins; major nitrogenous waste excreted in urine

uric acid

breakdown product of nucleic acids; nitrogenous waste excreted in the urine

creatinine

breakdown product of the skeletal muscle protein creatine; nitrogenous waste excreted in the urine

creatinine clearance

measurement of the rate at which creatinine is cleared from the blood by the kidney

principal cells

Cuboidal cells in the collecting duct; without microvilli
Help maintain the body's water and salt balance

intercalated cells of collecting duct

Alpha Intercalated Cells: secrete H+ and reabsorb HCO3

Beta Intercalated Cells: secrete HCO3 and reabsorbs H+

Maintain acid/base balance in the blood

colloid osmotic pressure (COP)

contribution of protein to blood osmotic pressure; draws water into capillary

Capsular hydrostatic pressure (CHP)

Hydrostatic pressure pushing back on glomerular membrane
Caused by existing fluid in Bowman's capsule
Opposes filtration

transport maximum (Tm)

upper limit to amount of material that carrier-mediated transport can move across the renal tubule

Detrussor

The _____ muscle is another name for the smooth muscle in the walls of the urinary bladder.

internal urethral sphincter

involuntary smooth muscle

external urethral sphincter

skeletal muscle, voluntary