Urinary System

kidneys

-filter blood and form urine, and contributes to homeostasis

-removes waste & forms RBCs

-regulates BP and pH

-secrete hormones & we cannot live without these functioning

-organ in the urinary system

ureters

-transports urine from kidneys to urinary bladder

-organ in the urinary system

urinary bladder

-collects and stores urine

-organ in the urinary system

urethra

-expels urine from urinary bladder to outside of body

-organ in the urinary system

description of kidneys

-reddish brown bean shaped organs with smooth surface

-perform several homeostatic functions for the body

kidney functions

-regulate volume and composition of body fluids

-removes excess water and electrolytes

-secretes erythropoietin (stimulates RBC production) and renin

increases BP

what does renin do?

location of kidneys

-right kidney sits lower than left for liver space

-renal capsule: surrounds outside of kidneys; inside is fat

-kidneys are retroperitoneal (behind parietal peritoneum)

renal cortex

outer region of kidney

renal sinus

hollow chamber in medial depression

renal medulla

-inner region that houses renal pyramids

-as pyramids tip they fill with urine, it reaches the renal papyla

renal pelvis

-funnel shaped sac; superior end of ureter

-major calyces: large tubes that merge to form renal pelvis

-minor calyces: small tubes that merge to form major calyces

renal columns

extensions of cortex that dip into medulla

hilum

entrance to renal sinus

nephrons

-functional units of kidney, each of which is a site of urine production

-composed of 2 parts: renal corpuscle and renal tubule

renal artery

-major kidney artery

-branches off abdominal aorta, enters kidney through hilum and sends blood into kidneys

-transports 15 to 30% of the cardiac output to the kidneys

segmental arteries

-major kidney artery

-branch off renal artery

interlobar arteries

-major kidney artery

-branch off segmental arteries, flow between renal pyramids

arcuate (arciform) arteries

-major kidney artery

-branch off interlobular arteries, arch around renal pyramids

cortical radiate arteries

-major kidney artery

-branch off arcuate arteries

smaller

all of the arteries of the kidneys get _________ as they branch off one another

afferent arterioles

branch off cortical radiate arteries; each enters a different nephron (“arrives”)

glomerulus

capillary cluster that branches from afferent arterioles; filters blood in each nephron

efferent arteriole

arises from merging of glomerular capillaries; transports blood that was not filtered by glomerulus (“exits”)

peritubular capillaries

-branches off efferent arterioles; surrounds renal tubules

-try to give nephrons a “hug”

-ensures all the good things in your blood are kept

flowchart of renal blood supply

abdominal aorta → renal artery → segmental artery → interlobar artery → arcuate artery → cortical radiate artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → cortical radiate vein → arcuate vein → interlobar vein → renal vein → inferior vena cava

renal corpuscle

-part of a nephron

-filtration happens in glomerulus which is the capillary cluster that filters blood and arises from afferent arteriole & drains into efferent arteriole

-Glomerular (Bowman’s) capsule: receives filtrate from glomerulus

renal tubule

-part of a nephron

-extends from glomerular capsule to collecting duct

-kidneys decide what stays/goes

-filtrate moves to Bowman’s capsule → proximal tubule → nephron loop (loop of Henle) → distal tubule

podocytes

-wraps around capillary

-allows H20, ions, & amino acids to pass through; keeps proteins

sequence of structures in urine formation

glomerulus → glomerular capsule → proximal tubule → nephron loop (descending) → nephron loop (ascending) → distal tubule → collecting duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra

collecting ducts; minor calyx

urine formation stops at the __________, and urine excretion begins at the _______

cortical nephrons

-majority of nephrons (85%)

-live almost completely in the renal cortex

-have short nephron loops

-renal corpuscles located near surface of kidney

-responsible for everyday filtration

juxtamedullary nephrons

-smaller percentage of nephrons (15%)

-have longer nephron loops that extend deep into kidney medulla

-renal corpuscles lie deep in renal cortex

-important in regulating water balance and urine concentration (darker yellow)

-more water = more concentrated

juxtaglomerular apparatus

-structure that regulates the secretion of the enzyme renin, and monitors BP and NaCl content of filtrate

-macula densa: closely packed cells of the ascending limb; monitors NaCl content of filtrate

-juxtaglomerular cells: vascular smooth muscle cells of afferent arteriole; monitors BP

-if either drops, renin is released

urine

-formed by nephrons and collecting ducts as they regulate composition of body fluids and removes waste from blood

-contains wastes, excess H20, and electrolytes

-3 processes: glomerular filtration, tubular reabsorption, and tubular secretion

glomerular filtration

-part of urine formation; 1st step

-capillaries make water and small molecules filtered, which then become tubular fluid

-filtration is passive, driven by pressure

-fenestrae: tiny opening in walls that helps permeability

-glomerular filtrate: substrate filtered in glomerulus into the capsule

filtration pressure

-main force that filters substances through glomerular capillaries and pushes fluid out

-glomerulus is made for pressure

-afferent arterioles have larger diameter than efferent arterioles

-resistance in efferent arterioles increases BP in glomerulus, therefore increasing filtration

forces favoring filtration

glomerular capillary hydrostatic pressure (BP)

forces opposing filtration

glomerular capillary colloid osmotic pressure & capsular hydrostatic pressure

glomerular filtration rate (GFR)

-measures how much fluid all functioning glomeruli are filtering over time

-average adult: 125 mL/min or 180 L/day

-only small percentage of filtrate is actually excreted as urine

autoregulation

-keeps GFR relatively constant

-increase in BP causes vasoconstriction of afferent arterioles

-”kidneys can adjust themselves”

-reduces blood flow to glomerulus, decreases GFR, maintains kidney function

hormonal control by cardiac hormones

-heart secretes atrial natriuretic peptide (ANP) which gets rid of salt, so when water follows salt the BP decreases

-heart also secretes ventricular natriuretic peptide (BNP) in response to increases BV and BP