A&P Exam 4

Describe the layers of the kidney

3 main layers: Renal fascia: outer layer of dense fibrous CT that anchors kidney & adrenal gland to surrounding structures Perirenal fat capsule: fatty mass that surrounds kidney and cushions it against blows Fibrous capsule: transparent capsule that prevents infections in surrounding regions from spreading to kidney

Trace the blood supply through the kidney

Aorta > renal artery > segmental artery > interlobar artery > arcuate artery > cortical radiate artery > afferent arteriole > glomerulus (capillaries) > efferent arteriole (drains into both) > cortical radiate vein and arcuate vein > interlobar vein > renal vein > inferior vena cava

Describe the mechanisms responsible for the medullary osmotic gradient including how structure of ascending and descending limb of the nephron create a gradient.

Countercurrent multiplier - interaction between flow of filtrate through ascending and descending libs of long nephron loops of juxtamedullary nephrons Countercurrent exchanger - flow of blood through ascending and descending portions of vasa recta

Explain the difference between excretion and tubular secretion

Excretion: waste products produced by metabolism excreted from body through urine. Include nitrogenous wastes urea, form protein catabolism, and uric acid, from nucleic acid metabolism. Tubular secretion: process of selectively moving substances from blood into filtrate. Like tubular reabsorption, occurs along length of tubule and collecting duct.

List and define the three major renal processes

Glomerular filtration, Tubular reabsorption, and Tubular secretion

Describe the forces (pressures) that counteract glomerular filtration

Hydrostatic pressure in capsular space is pressure exerted by filtrate in glomerular capsule. HPcs much higher than hydrostatic pressure surrounding most capillaries because filtrate is confined in small space with narrow outlet Colloid osmotic pressure in glomerular capillaries is pressure exerted by proteins in blood

substances that are secreted by tubular secretion

Moves selected substances (H+, K+, NH4+, creatinine) from peritubular capillaries through tubule cells into filtrate.

In which part of the nephron does the most reabsorption occur?

Proximal convoluted tubules are by far the most active reabsorbers. Usually reabsorbs all glucose and amino acids in filtrate and 65% of Na+ and water. Bulk of electrolytes are reabsorbed by time filtrate reaches nephron loop. Nearly all uric acid and about half of urea reabsorbed in proximal tube.

intrinsic controls of the glomerular filtration rate

Renal autoregulation, Myogenic mechanism, and Tubuloglomerular feedback mechanism

sodium transport across apical membrane

Sodium transport across apical membrane - active pumping of Na+ from tubule cells results in strong electrochemical gradient that favors its entry at apical face via secondary active transport carriers or via facilitated diffusion through channels. Occurs because (1) pump maintains intracellular Na+ concentration at low levels, and (2) K+ pumped into tubule cells almost immediately diffuses out into interstitial fluid via leakage channels, leaving interior of tubule cell w/net (-) charge

Describe the mechanisms (including hormones) underlying water and solute reabsorption from the renal tubules into the peritubular capillaries

Sodium transport across apical membrane, Secondary active transport, Passive tubular reabsorption of water, and Passive tubular reabsorption of solutes

How do the kidneys regulate urine concentration and volume?

The kidneys create and use an osmotic gradient to regulate urine concentration and volume

How does the body transport, store, and eliminate urine?

The ureters, bladder, and urethra transport, store, and eliminate urine

Secondary active transport

apical carrier moves Na+ down its concentration gradient as it cotransports another solute. Cotransported solutes move across basolateral membrane by facilitated diffusion via other transport proteins before moving into peritubular capillaries

Renin-angiotensin-aldosterone mechanism

body's main mechanism for increasing blood pressure. Low blood pressure causes granular cells of juxtaglomerular complex to release renin. Three pathways regulate granular cells: Sympathetic nervous system Activated macula densa cells Reduced stretch

Describe the gross anatomy of the kidney

frontal section consists of three distinct regions - cortex, medulla, pelvis. The renal cortex is most superficial region (granular appearance). Renal medulla is deep to the cortex and exhibits cone-shaped tissue masses called medullary/renal pyramids (appear striped, darker, reddish-brown) - each pyramids' base faces toward cortex, and its apex/papilla points internally. Renal columns separate the pyramids. Renal pelvis - funnel-shaped tube, continuous w/ureter leaving hilum. 2 or 3 major calyces branch from pelvis, each subdivides and forms several minor calyces - cup-shaped areas that enclose papillae. Calyces collect urine.

ADH

inhibits diuresis (urine output). Makes principal cells of collecting ducts more permeable to water by causing aquaporins to be inserted into their apical membranes. Amount of ADH determines number of aquaporins, thus amount of water that's reabsorbed there. When body is overhydrated, extracellular fluid osmolality decreases, decreasing ADH secretion by posterior pituitary and making collecting ducts relatively impermeable to water. ADH also increases urea reabsorption by collecting ducts.

juxtaglomerular complex

is the region where most distal portion of ascending limb of nephron loop lies against afferent arteriole feeding glomerulus.

extrinsic controls of the glomerular filtration rate

it maintains systemic blood pressure Sympathetic nervous system controls, and Renin-angiotensin-aldosterone mechanism

tubular secretion

process of selectively moving substances from blood into filtrate. Like tubular reabsorption, it occurs along length of tubule and collecting

tubular reabsorption

process of selectively moving substances from filtrate back into blood. It takes place in renal tubules and collecting ducts. Tubular reabsorption reclaims almost everything filtered - all of glucose and amino acids, and some 99% of water, salt, and other components. Anything that is not reabsorbed becomes urine

Atrial natriuretic peptide (ANP)

reduces blood Na+ which decreases blood volume/pressure. Released by cardiac atrial cells when blood volume/pressure is elevated. Lowers blood Na+ content and directly inhibits Na+ reabsorption at collecting ducts

Describe how sodium and water reabsorption are regulated in the distal tubule and collecting duct.

regulated by ADH, Aldosterone, and Atrial natriuretic peptide (ANP)

name components in the order that the filtrate passes through them

renal corpuscle > proximal convoluted tubule > loop of Henle > distal convoluted tubule > collecting tubule > collecting duct

Passive tubular reabsorption of solutes

solutes follow solvent, which explains passive reabsorption of solutes present in filtrate. Since lipid-soluble compounds can generally pass through membranes, they'll follow concentration gradients and be reabsorbed, even if this is not 'desirable'. As Na+ ions move through tubule cells into peritubular capillary blood, also establish electrical gradient that favors passive reabsorption of anions to restore electrical neutrality in filtrate and plasma

glomular filtration

takes place in renal corpuscle and produces cell- and protein-free filtrate

Describe the anatomy of a nephron

they are the structural and functional units of kidneys. Each kidney contains over 1 million of these tiny blood-processing units, carry out processes that form urine. Each has renal corpuscle (located in renal cortex) and renal tubule (go from cortex to medulla to cortex).

Passive tubular reabsorption of water

water moves by osmosis into peritubular capillaries. Aquaporins aid this process by acting as water channels across plasma membranes.

Aldosterone

"salt-retaining hormone" which promotes the retention of Na+ by the kidneys. na+ retention promotes water retention, which promotes a higher blood volume and pressure

tubuloglomerular feedback mechanism

'directed' by macula densa cells of juxtaglomerular complex. These cells respond to filtrate NaCl concentration. When GFR increases, there's not enough time for reabsorption and concentration of NaCl in filtrate remains high. Macula densa respond to high levels by releasing vasoconstrictor chemicals that cause intense constriction of afferent arteriole, reducing blood flow into glomerulus. This drop decreases NFP and GFR, slowing flow of filtrate and allowing more time for filtrate.

sympathetic nervous system controls

(extrinsic controls) when blood pressure falls, norepinephrine released by sympathetic nerve fiber causes vascular smooth muscle to constrict, increasing peripheral resistance and bringing blood pressure back up toward normal: baroreceptor reflex - afferent arterioles also constrict which decreases GFR and helps restore blood volume and pressure to normal

Renal autoregulation

(intrinsic control) kidney can maintain nearly constant GFR despite fluctuations in systemic arterial blood pressure

myogenic mechanism

(intrinsic control) reflects property of vascular smooth muscle - it contracts when stretched and relaxes when not stretched. Rising systemic blood pressure stretches vascular smooth muscle in arteriolar walls, causing afferent arterioles to constrict. This constriction prevents glomerular blood pressure from rising to damaging levels. Declining systemic blood pressure causes dilation of afferent arterioles and raises glomerular hydrostatic pressure. Maintain normal NFP and GFR

Describe the forces (pressures) that promote glomerular filtration

Hydrostatic pressure in glomerular capillaries is essentially glomerular blood pressure. It's chief force pushing water & solutes out of blood & across filtration membrane. Blood pressure in glomerulus is extraordinarily high and remains high across entire capillary bed. This is because glomerular capillaries are drained by high-resistance efferent arteriole whose diameter is smaller than afferent arteriole that feeds them. Filtration occurs along entire length of each glomerular capillary and reabsorption does not occur as it would in other capillary beds

Describe the importance of tubular secretion

Important for: Disposing of substances, such as certain drugs and metabolites, that are tightly bound to plasma proteins Eliminating undesirable substances or end products that have been reabsorbed by passive processes Ridding body of excess K+ Controlling blood pH

Compare juxtamedullary and cortical nephrons

Juxtamedullary: originate close to cortex-medulla junction, and they play an important role in kidney's ability to produce concentrated urine. Have long nephron loops that deeply invade medulla, and their ascending limbs have booth thin and thick segments Cortical: account for 85% of nephrons in kidneys. Except for small parts of their nephron loops that dip into outer medulla, they are located entirely in cortex

Compare the length and functions of the male urethra with those of the female

Male urethra is significantly longer than that of female's, thus, why it is easier for females to contract a UTI. Urine and semen come out of the tip of the male's penis, while only urine comes from the females' urethra.

Define micturition and describe its neural control. Include description of how sphincters are involved.

Micturition (voiding) - act of emptying urinary bladder. As urine accumulates, distension of bladder activates stretch receptors in its walls. Impulses form activated receptors travel via visceral afferent fibers to sacral region of spinal cord. Visceral afferent impulse, relayed by sets of interneurons, excite parasympathetic neurons and inhibit sympathetic neurons.

Describe the general location, structure, and function of the ureters, urinary bladder, and urethra.

Ureters - convey urine form kidneys to bladder; each begins at level of L2 as continuation of renal pelvis, then descends behind peritoneum and runs obliquely through posterior bladder wall, this arrangement prevents backflow of urine because any increase in bladder pressure compresses and closes distal ends of ureters Mucosa - transitional epithelium that's continuous with mucosae of kidney pelvis superiorly and bladder medially Muscularis - two smooth muscle sheets: internal longitudinal layer and external circular layer. Additional smooth muscle layer, external longitudinal layer, appears in lower third of ureter. Adventitia covering ureter's external surface is typical fibrous CT Bladder - smooth, collapsible, muscular sac that stores urine temporarily. Located retroperitoneally on pelvic floor just posterior to pubic symphysis. Has three layers: mucosa containing transitional epithelium, thick muscular layer, and fibrous adventitia. Urethra - thin-walled muscular tube that drains urine form bladder and conveys it out of body. Epithelium of its mucosal lining is mostly pseudostratified columnar epithelium

Explain how dilute and concentrated urine are formed. Include the role of ADH.

When dehydrated, posterior pituitary releases large amounts of ADH and solute concentration of urine rises, concentration of interstitial fluid in deepest part of medulla. Up to 99% of water in filtrate is reabsorbed and returned to blood and only half liter/day of highly concentrated urine is excreted. This process and ability our body has is critically tied to our ability to survive for a limited time w/out water. When overhydrated, ADH production decreases and osmolality of urine falls as low as 100 mOsm. If aldosterone is present, DCT and collecting duct cells can remove Na+ and selected other ions from filtrate, making urine that enters renal pelvis even more dilute.