A&P 2 Unit 3: Urinary System

What are the functions of the urinary system?

1. excretion of waste products from bodily fluids

2. elimination of waste

3. homeostatic regulation of volume and concentration of blood plasma

what are the essential homeostatic funtions?

1. regulating blood volume and pressure by adjusting volume of water lost in urine through the use of hormones EPO and Renin

2. regulating plasma concentrations of Na, K, Cl, and other ions

3. helps to stabilize blood pH, controls loss of H ions and bicarbonate ions in urine

4. conserves valuable nutrients, prevents their excretion in urine

5. assists the liver by detoxifying poisons and deaminating amino acids

what do the kidneys do?

produce urine

where are the adrenal glands located?

on top of the kidneys

what is the urinary tract made of?

2 ureters

urinary bladder

urethra

what do the ureters do?

transport urine from kidneys to bladder

what does the bladder do?

stores urine temporarily

what does the urethra do?

transports urine from the bladder to outside the body

what does the renal fascia do?

anchors kidney to surrounding structures, outer most structure

what is the adipose capsule?

adipose tissue that surround the kidneys

what is the renal capsule?

covers the outer surface of the kidney

what is the hilum?

point of entry for artery, nerve, and exit for vein and ureters

what is the renal sinus?

an internal cavity inside of the kidney

what is the renal cortex?

the outer portion of the kidney

what is the renal medulla?

the inner portion of the kidney

what are the renal pyramids?

6-18 triangle shaped structures in the medulla

what is the renal papilla?

tip or point of pyramids, projects into renal sinus

what are the renal columns?

bands of tissue in between the pyramids

what does the minor calyx do?

collects urine from the papilla

what does the major calyx do?

collects urine from 4 to 5 minor calyx

what are nephrons?

functional unit of the kidneys

what is the order of renal blood flow?

Renal artery → Segmental arteries → Interlobar arteries → Arcuate arteries → Interlobular arteries → Afferent arterioles → Glomerulus → Efferent arteriole → Peritubular capillaries* → Interlobular veins → Arcuate veins → Interlobar veins → Renal vein

what do renal nerves do?

1. adjusts the rate if urine formation by altering blood flow and pressure at nephron

2. stimulates renin which stimulates water and salt reabsorption at nephron

what are cortical nephrons?

located totally in the superficial cortex of the kidney

what are juxtamedullary nephrons?

have long loops of henale that extend deep into the medulla, produce concentrated urine

what is the vasa recta?

long capillaries that parallel loop of henle in juxtamedullary nephrons

bowman’s capsule

cup-shaped outer wall of renal corpuscle (parietal epithelium)

capsular space

space between parietal and visceral epithelium

glomerulus

interconnected capillaries inside the renal corpuscle (visceral epithelium)

afferent arteriole

blood into the glomerulus

efferent arteriole

blood out of the glomerulus

podocytes

(cells in visceral epithelium) – contain feet known as Pedicels

filtration slits

gaps between pedicels

proximal convoluted tubule (PCT)

First segment of the renal tubule

• tubular fluid- fluid inside renal tubule

• peritubular fluid- interstitial fluid surrounding renal tubule

Reabsorption of nutrients, ions, water & plasma proteins is the primary function of PCT

loop of henle

Descending limb connects to PCT

Ascending limb connects to DCT

Thick segment- refers to size of cells not the diameter of lumen, pumps sodium & chloride ions out of fluid

Thin segment- freely permeable to water

distal convoluted tubule (DCT)

Passes between afferent and efferent arterioles

Active secretions of ions, acids, drugs and toxins

Selective reabsorption of Na ions, Ca ions, & water

juxtaglomerular apparatus

secretes hormones EPO and Renin

macula densa

cluster if cells along DCT

juxaglomerular cells

smooth muscle fibers

collecting duct

Transports tubular fluid from nephron to renal pelvis

Adjusts the final composition, concentration, and volume of urine

Several collecting ducts unite to form a papillary duct

PAPILLARY DUCT → MINOR CALYX → MAJOR CALYX

purpose of organic waste products

produce urine to regulate volume and composition of blood

urea

most abundant organic waste, most of it from breaking down amino acids, 21 g/day

creatinine

generated in skeletal muscle from the break down of creatine phosphate, 1.8g/day, all is excreted

uric acid

formed from recycling nitrogenous bases RNA, 480mg/day

filtration

blood pressure forces water & solutes across wall of the glomerulus

reabsorption

removal of water & solutes from the filtrate, occurs after filtrate has left the renal corpuscle

secretion

transport of solutes into renal tubules, back up process to filtration in order to remove all undesirable materials from blood plasma

glomerulus / renal corpuscle

only site of filtration

generates 180L/ day of filtrate

same composition as blood plasma without plasma proteins

plasma proteins and RBCs can not leave the glomerulus

glomerular hydrostatic pressure (GHP)

• is the blood pressure in the glomerular capillaries, (about 50 mmHg)

• tends to push water & solutes out of plasma

capsular hydrostatic pressure (CsHP)

• pressure inside the nephron & conducting system, (15mmHg)

• wants to push water & solutes back into plasma – opposes GHP

blood colloid osmotic pressure (BCOP)

• tends to pull water back into plasma due to plasma proteins in glomerulus (25mmHg)

• opposes GHP

filtration pressure (FP)

equals sum of all three pressures, this is the pressure that forces water and dissolved materials out of the glomerulus and into the capsular space → into renal tubule

glomerular fitration rate (GFR)

• amount of filtrate the kidneys produce each minute (125 ml/ min)

• kidney filtration will stop if BP at glomerulus drops 20%

• decline in GFR can lead to renal failure

autoregulation

1. dilates afferent arterioles

2. dilates glomerular capillaries

3. constricts efferent arterioles

elevates glomerular BP

hormonal regulation

decline in BP triggers release if renin from juxtaglomerular apparatus

nephron

causes constriction of efferent arteriole, directly stimulates PCT to reabsorb Na & water

adrenal gland

causes secretion of aldosterone à increases Na reabsorption in DCT & collecting duct

CNS

increases thirst, release of ADH → increases water absorption in DCT & collecting duct, increases cardiac output

peripheral capillary beds

vasoconstricts arterioles → increases BP throughout body

autonomic regulation

sympathetic activation causes vasoconstriction of afferent arteriole causing a decrease in GFR (overrides local autoregulation), (do not urinate when running)

reabsorption

recover useful materials that have left the bloodstream in the filtrate

secretion

ejects waste products and toxins that did not leave the bloodstream at the glomerulus

proximal convoluted tubule (PCT)

• 66% of the filtrate is reabsorbed at the PCT

• Almost all of the glucose, amino acids and other organic nutrients in the filtrate are reabsorbed

loop of henle

• Reabsorbs 15 %, about half of the remaining water and 2/3 of the Na & Cl ions

• Uses countercurrent concentration- exchange between thin descending limb & thick ascending limb with tubular fluid moving in different directions

thin limb of loop of henle

permeable to water but relatively impermeable to solutes

thick limb of loop of henle

impermeable to water and to solutes, Pumps Na & Cl ions out of tubular fluid

(Almost 2/3 of ions are pumped out)

distal convoluted tubule (DCT)

• Only about 15-20% of the filtrate gets to this point

• This fluid no longer resembles plasma

  • urea is now makes up a significant proportion

• The hormone aldosterone causes more Na to be reabsorbed  water follows salt

  • however this is associated with a potassium ion loss

• DCT is also site for Ca reabsorption

  • regulated by parathyroid hormone

secretion at the DCT

• Potassium (K) is secreted in exchange for Na ions

• Hydrogen ions (H) are also secreted at this time

• H removal is coupled with bicarbonate ion production to help with blood pH (stimulated by aldosterone)

• DCT deamination of amino acids eliminates H ions & ammonium ions  produces bicarbonate ions for the bloodstream

collecting duct

• Receives tubular fluid from many nephrons and carrys it toward the renal sinus

• Aldosterone continues to cause Na reabsorption

• Bicarbonate ions are reabsorbed in exchange for chloride ions

• ADH makes DCT & collecting ducts permeable to water (usually impermeable to water) and accounts for the reabsorption of the remaining 15% of water

• BY THIS TIME 99% of the 180 L of filtrate has been reabsorbed

vasa recta

carry both water and solutes out of the medulla at about the same rate as reabsorption and osmosis takes place in the medulla

urine production

• A healthy adult typically produces 1200ml of urine a day

• pH = 4.5 to 8 (average = 6)

• specific gravity = 1.003 to 1.030

• water content = 93% to 97%

• color = clear yellow

• urine is sterile (no bacterial content)