Chapter 24: The Urinary System

processes of urine formation

1. Glomerular filtration: blood pressure forces water and solutes across filtration membrane 2. Tubular reabsorption: the movement of water and solutes from the tubular fluid and into the blood of the peritubular capillaries of vasa recta. 3. Tubular secretion: the movement of solutes out of the blood within the peritubular capillaries and vasa recta and into the tubular fluid. (secretion can be primary means of excretion for some compounds, including many drugs)

juxtamedullary nephrons

15% of nephrons, long loops of Henle that extend deep into medulla, allows for production of concentrated urine, efferent arteriole supplies vasa recta; glomerulus close to cortex-medulla junction

cortical nephrons

85% of nephrons; shorter loops of Henle, efferent arteriole supplies peritubular capillaries; glomerulus further from cortex-medulla junction.

renal tubule

long, tubular passageway that modifies filtrate through tubular reabsorption & secretion.

middle muscularis

made up of detrusor muscle; the portion of the detrusor muscle that surrounds the neck of the bladder forms an internal sphincter muscle.

macula densa

is a region where cells of thick ascending limb contact granular cells; detect changes in NaCl concentration in filtrate; signal granular cells to release renin.

renal cortex

light in color and has a granular appearance; outer layer of areolar CT; contact renal capsule

aldosterone

Sodium reabsorption regulated by hormones: • Aldosterone: increases Na reabsorption • Atrial natriuretic peptide (ANP): inhibits Na reabsorption by PCT and DCT as well as the release renin; results in more Na and water being excreted in urine. • Water reabsorption regulated by ADH and is independent of Na reabsorption; ADH acts on principal cells of collecting tubules and ducts to insert more aquaporins to facilitate more water reabsorption (facultative water reabsorption) Aldosterone: released by adrenal cortex in response to angiotension II; increases sodium reabsorption in DCT & collecting tubules

renal pelvis

a flat, funnel-shaped tube, is simply the expanded superior part of the ureter.

urinary bladder

a hollow, distensible, muscular organ lying in the pelvic cavity • Inner mucosa epithelium (transitional epithelium): mucosa lining has folds or rugae that disappear as bladder fills • Middle muscularis: made up of detrusor muscle; the portion of the detrusor muscle that surrounds the neck of the bladder forms an internal sphincter muscle. • The outer adventitia of areolar connective tissue. • The internal floor of the bladder includes the trigone, openings of the ureters and urethra. • Funnels urine into the urethra when bladder contracts.

urine

a sterile excretion of filtered & processed blood plasma • Typically 95% water & 5% solutes • Solutes include NaCl, K, Hg, H, Ca, SO4, H2PO4, Urea, and NH4 • 1-2 L urine per day on average • 0.5 L minimum urine daily to remove wastes, anything less accumulates in blood.

granular cells (juxtaglomerular cells)

are modified smooth muscle cells of the afferent arteriole located near the entrance of renal corpuscle; contract when stimulated by stretch or the sympathetic NS and they synthesize, store, and release renin.

outer adventitia

areolar connective tissue.

glomerular filtration

blood pressure forces water and solutes across filtration membrane

urea

breakdown of amino acids during normal recycling of the body's proteins

renal medulla

consists of cone-shaped masses called renal pyramids; inner region of kidney, contains 6-18 renal pyramids

renal fascia

contains an external layer of fat, the pararenal fat.

visceral layer

covers glomerular capillaries & contains large podocytes that wrap around basement membrane

visceral epithelium

covers glomerular capillaries and contains large, branching cells that wrap around a basement membrane.

perirenal

cushion the kidney against blows and help hold the kidneys in place.

major calices

divides to form several minor calices- cup-shaped tubes that enclose the papillae of the pyramids.

renal pyramids

each pyramid contains collecting ducts that converge at renal papillae and drain into renal pelvis.

renal corpuscle

enlarged, bulbous region of nephron responsible for filtration of blood

urethra

epithelial-lined fibromuscular tube; tube that conveys urine from the urinary bladder to the outside; a muscular tube with urethral glands that secrete mucus into the urethral canal. • Female- 4cm long primarily stratified squamous ET • Male- 19cm long; prostatic urethra (transitional ET) • Intermediate/Membranous urethra: stratified columnar transitions to pseudostratified columnar & passes through urogenital diaphragm • Spongy urethra: pseudostratified columnar transitions to stratified squamous ET; travels through penis • Two urethral sphincters control release of urine: internal urethral sphincter is involuntary, controlled by parasympathetic ANS activity; external urethral sphincter is voluntary, controlled by somatic motor division.

renal capsule

fibrous covering of each kidney

pedicels

foot-like projections form podocytes, form filtration slits, each of which is covered by a thin slit of diaphragm.

creatinine

formed by the breakdown of creatine phosphate, a molecule in muscle that stores energy for the manufacture of adenosine triphosphate (ATP).

glomerular capsule

forms outer wall of renal corpuscle and encapsulates the glomerular capillaries.

renin

hormone that converts angiotensinogen into angiotensin I • Angiotensin: converting enzyme (ACE) converts angiotensin I into angiotensin II (potent vasoconstrictor) (stimulates release of ADH & aldosterone) (activates thirst center) (decrease GFR- glomerular filtration rate)

internal floor

includes the trigone, openings of the ureters and urethra. • Funnels urine into the urethra when bladder contracts.

renal column

inward extensions of the renal cortex, separate adjacent pyramids.

kidneys

maintain the purity and chemical constancy of the blood and the other extracellular body fluids. Filters many liters of fluid, sending toxins, metabolic wastes, excess water, and excess ions out of the body in urine while returning needed substances from the filtrate to the blood. • Urea- breakdown of amino acids during normal recycling of the body's proteins • Uric acid- results from the turnover of nucleic acids • Creatinine- formed by the breakdown of creatine phosphate, a molecule in muscle that stores energy for the manufacture of adenosine triphosphate (ATP). • Regulate the volume and chemical makeup of the blood by maintaining the proper balance of water and salts and of acids and bases. • Other organs: ureters, urinary bladder, and the urethra • Produces & secretes erythropoietin + renin • Formation of calcitriol (vitamin D); kidneys synthesize final enzyme in pathway; calcitrol increases and Ca absorption by small intestines.

renal hilum

medial indentation, point of entry for renal artery and nerves and point of exit for renal vein and ureter.

nephron

microscopic functional unit of kidney

inner mucosa epithelium

mucosa lining has folds or rugae that disappear as bladder fills

ureters

muscular tubes extending from the kidneys to the base of the urinary bladder. • The wall of the ureter is composed of three layers: mucosa, muscularis, and adventitia. • Longitudinal and circular smooth muscles make up muscularis layer • Additional external longitudinal layer of muscle in distal portion of ureters. • Mucosa formed by transitional epithelium (distensible and impermeable)

glomerulus

network of about 50 intertwining capillaries; glomerulus capillaries are fenestrated capillaries- large diameter pores to allow filtration of blood.

trigone

openings of the ureters and urethra.

ascending limb

permeable to Na but not water

descending limb

permeable to water but not Na

spongy urethra

pseudostratified columnar transitions to stratified squamous ET; travels through penis

uric acid

results from the turnover of nucleic acids

capsular space

separates the parietal and visceral epithelia.

parietal epithelium

simple squamous epithelium, which is continuous with the visceral epithelium that covers glomerular capillaries.

intermediate/membranous urethra

stratified columnar transitions to pseudostratified columnar & passes through urogenital diaphragm

tubular secretion

the movement of solutes out of the blood within the peritubular capillaries and vasa recta and into the tubular fluid. (secretion can be primary means of excretion for some compounds, including many drugs)

tubular reabsorption

the movement of water and solutes from the tubular fluid and into the blood of the peritubular capillaries of vasa recta.

filtration membrane

thin, porous & negatively charged membrane formed by endothelium of glomerular capillaries & the visceral layer of Bowman's capsule

fibrous (renal) capsule

thin, tough layer of dense connective tissue adheres directly to the kidney's surface, maintaining its shape and forming a barrier that can inhibit the spread of infection from the surrounding regions.

renal papillae

tip of each renal pyramid that projects into renal sinus

micturition

urine leaves the bladder by the micturition reflex; stretch receptors in bladder wall stimulated as bladder fills; as a result you become consciously aware of the pressure in your bladder. • Adequate stimulation causes parasympathetic neurons to stimulate sustained contraction of the detrusor muscle, elevating pressure in bladder. • When these contractions become strong enough, the internal urethral sphincter is forced open. • Relaxation of the external urethral sphincter is necessary for micturition to occur.

atrial natriuretic peptide

volume • Opposes action of Aldosterone • Inhibits Na reabsorption on DCT & collecting tubules.

juxtaglomerular apparatus

• Area of specialized contact between renal tubule and afferent arteriole; important structure in regulating blood pressure

collecting ducts

• Each nephron drains into a collecting tubule • Several collecting tubules drain into collecting ducts which further modifies filtrate. • Simple cuboidal ET thickens to simple columnar ET in papillary ducts • Collecting ducts merge to form papillary ducts which empty into minor calyces. • Contain two types of specialized cells: • Principal cells: respond to aldosterone and ADH, varying secretion potassium in response to aldosterone. • Intercalated cells have lots of mitochondria for reabsorption and secretion of ions; play a role in regulating pH of urine

loop of henle (nephron loop)

• Extends into medulla • Increases osmolarity of interstitial fluid of medulla to allow for countercurrent exchange & concentration of filtrate. • Thick segments have cuboidal epithelium, thin segments have simple squamous epithelium. • Descending limb- permeable to water but not Na • Ascending limb- permeable to Na but not water

External anatomy of the kidney

• Lie retroperitoneal in the superior lumbar region of the posterior abdominal wall; extend from the level of the 11th or 12th thoracic vertebra superiorly to the 3rd lumbar vertebra inferiorly and receive protection from the lower two ribs. • Lateral surface is convex; medial surface is concave; vertical cleft called the renal hilum: vessels, ureters, and nerves enter and leave the kidney. • Fibrous capsule: thin, tough layer of dense connective tissue adheres directly to the kidney's surface, maintaining its shape and forming a barrier that can inhibit the spread of infection from the surrounding regions. • Renal fascia contains an external layer of fat, the pararenal fat. • Perirenal and pararenal fat layers cushion the kidney against blows and help hold the kidneys in place.

proximal convoluted tubule

• Reabsorption (NaCl, obligatory water reabsorption, glucose, amino acids, Potassium, HC03, urea • Secretion: uric acid and organic acids • Located in renal cortex • Cuboidal epithelial cells with long, abundant microvilli • Highly folded basolateral cell surfaces with lots of ion pumps; abundant mitochondria; bulk of reabsorption & secretion occurs (obligatory)

antidiuretic hormone (vasopressin)

• Released by posterior pituitary, produced by hypothalamus • Increase water reabsorption (principal cells of collecting tubes & ducts) by inserting more aquaporins

Flow of blood to the kidney

• Renal artery divides into 5 segmental arteries that enter the renal hilum & divide into interlobar arteries that radiate out through renal columns & give rise to arcuate arteries that arch along corticomedullary junction & divide into cortical radiate arteries that supply cortical tissues & give rise to the afferent arterioles that supply blood to glomerulus. • The efferent arteriole receives blood from glomerulus & gives rise to 2 capillary networks: peritubular capillaries & vasa recta.

distal convoluted tubule

• Secretion of ions and acids • Selective reabsorption of Na in response to aldosterone and ANP • Ca in response to PTH • Water in response to ADH • Located in renal cortex • Cuboidal epithelium with shorter fewer microvilli • Highly folded basolateral surfaces with lots of ion pumps & mitochondria; selective reabsorption & secretion occur under the action of hormones & physiological needs of the body.

mesangial cells

• Specialized cells located within and between the capillary loops of the glomerulus • ANP (atrial natriuretic peptide): relaxes mesangial cells to increase filtration membrane surface area. • Angiotension II stimulates myofilaments in mesangial cells to contract decreasing surface area of filtration membrane.