Renal & Digestive Systems

renal columns

renal pyramids

renal capsule

renal cortex

renal artery

renal vein

renal pelvis

ureter

renal medulla

major calyx

minor calyx

glomerulus

glomerular capsule

proximal convoluted tubule (PCT)

descending limb of loop of Henle

nephron loop

ascending limb of loop of Henle

distal convoluted tubule (DCT)

collecting duct of the nephron

the afferent arteriole in the kidney

carries blood to the glomerulus

the efferent arteriole in the kidney

carries blood away from the glomerulus

What are peritubular capillaries?

Tiny blood vessels that travel alongside nephrons.

What is the function of peritubular capillaries?

Allow reabsorption and secretion between blood and the inner lumen of the nephron.

the nephron is the

functional unit of the kidney

what does the urinary system consist of

2 kidneys, 2 ureters, urinary bladder, urethra

urine consists of

excess water, ions, metabolic wastes, and some toxic substances

What is one major function of the kidneys?

Removal of waste products from blood

How do the kidneys help maintain blood pH?

By regulating the balance of acids and bases in the blood

What role do the kidneys play in fluid and electrolyte balance?

They maintain the balance of fluids and electrolytes in the body

How do the kidneys regulate blood pressure?

By releasing renin, which converts angiotensinogen to angiotensin I

What vitamin do the kidneys activate?

Vitamin D

where are the kidneys located

retroperitoneal, in the nonmesenteric region

the retroperitoneal is

located behind the peritoneum

what surrounds the kidneys to cushion them

adipose tissue

renal fascia

CT which anchors the kidneys to the abdominal wall

the hilum of the kidneys is where

renal arteries and nerves enter, and renal veins and ureter exit the kidneys

what are the two parts that make up the renal corpuscle

glomerulus and the glomerular capsule

podocyte

These cells form a porous membrane surrounding the endothelial cells of the glomerulus.

what are the two substances that CANNOT be filtered by the kidneys

large proteins and blood cells

filtration membranes of the glomerulus

first step in urine formation - where the blood is filtered

juxtaglomerular apparatus

Regulates blood pressure and filtration rate - site of renin production

What are juxtaglomerular cells?

The cells of the afferent artery at the juxtaglomerular apparatus.

What is the function of juxtaglomerular cells?

They are baroreceptors that secrete renin upon sensing a decrease in blood pressure.

what are the four parts of the renal tubule

proximal convoluted tubule, nephron loop, distal convoluted tubule, collecting duct

juxtamedullary nephrons

only 15% of nephrons, extend deep into the medulla

cortical nephrons

near the periphery of the cortex, do not extend deep into the medulla

renal corpuscle

filtration part of the nephron

fenestrae

- small holes in glomerular capillary walls - filter out fluid (glomerular filtrate)

filtration membrane

interface between the glomerulus and the nephron

the three steps in urine formation

glomerular filtration, tubular reabsorption, tubular secretion

filtration of the kidneys

movement of fluid from blood to filtrate at the glomerulus capsule

filtrate

water, small molecules, and ions that can pass through a membrane

renal fraction

part of total cardiac output that passes through the kidneys

what percent of the cardiac output passes through the kidneys

21% (average)

renal blood flow rate

rate of whole blood flow through the kidneys

renal blood flow rate formula

cardiac output * renal fraction

what is the average renal blood flow rate

1176 ml/min

renal plasma flow rate

renal blood flow rate X fraction of blood that is plasma: 650 mL/min

Glomerular Filtration Rate (GFR)

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

what is the total amount of filtrate produced by the kidneys in one day

180 L

glomerular filtration rate formula

renal plasma flow rate * filtration fraction

filtration fraction

part of plasma that is filtered into lumen of Bowman's capsules; average 19%

average urine production per day

1-2 L. Most of filtrate must be reabsorbed

What is filtration pressure?

The pressure gradient responsible for filtration.

What does filtration pressure do?

It forces fluid from the glomerular capillary across the membrane into the lumen of the glomerular capsule.

pressures that contribute to filtration pressure

glomerular capillary pressure, capsule hydrostatic pressure, blood colloid osmotic pressure

glomerular capillary pressure (GCP)

blood pressure inside capillary, moves fluid out of capillary and into the glomerular capsule

Capsule hydrostatic pressure (CHP)

pressure of filtrate already in the lumen of the glomerular capsule

blood colloid osmotic pressure (BCOP)

osmotic pressure caused by proteins in blood

capsule hydrostatic pressure is a(n)

inward pressure movement - forces filtrate back into glomerular capillaries

blood colloid osmotic pressure is a(n)

inward pressure movement

BCOP is always greater at the

end of the glomerular capillary than at the beginning

Net filtration pressure is equal to

10 mmHg

what two ways are required to regulate glomerular filtration rate

intrinsic and extrinsic regulation

intrinsic regulation of the GFR is regulated via

autoregulation

extrinsic regulation of the GFR is regulated via

sympathetic nervous system and secreted hormones

myogenic mechanism

mechanism for renal autoregulation in which smooth muscle cells in afferent arterioles contract in response to elevated blood pressure

tubuloglomerular feedback mechanism

Mechanism for renal autoregulation in which the macula densa senses increased load and causes constriction of the nearby afferent arteriole, increasing resistance to maintain constant blood flow.

when does extrinsic regulation of the glomerular filtration rate occur

severe conditions such as dehydration or hemorrhage

sympathetic stimulation of the GFR

constricts arteries and afferent arterioles --> decreasing renal blood flow and filtrate formation

how does the secretion of renin affect GFR

forms angiotensin II which stimulates vasoconstriction, decreasing blood flow to the kidney

where does most reabsorption occur in the nephron

proximal convoluted tubule

what is the descending loop of the nephron most permeable to

water

what is the ascending loop of the nephron most permeable to

Na+, NOT permeable to water

the distal convoluted tubule and collecting ducts water permeability are regulated by

aldosterone, antidiuretic hormone (ADH) and atrial nitruiretic peptide

range of urine concentrations

65 mOsm/kg - 1200 mOsm/kg

what three factors affect volume and concentration of urine

countercurrent mechanisms, medullary concentration gradient, and hormonal mechanisms

countercurrent mechanism

Occurs when fluid flows in opposite directions, materials may be exchanged as they pass

What is the countercurrent multiplier?

A mechanism that enhances the concentration of urine in the kidneys.

Where does the countercurrent multiplier occur?

In the nephron loop.

What is the result of the countercurrent multiplier in the medulla?

It creates a high concentration of solutes in the interstitial fluid.

countercurrent exchanger

maintains the high solute concentration in the interstitial fluid in the vasa recta

vasa recta

The capillaries that surround the tubules of the nephron. Reclaims reabsorbed substances, such as water and sodium ions.

what is the purpose of the countercurrent multiplication in the kidneys

create an osmotic gradient to reabsorb water from tubular fluid and produce concentrated urine

the proximal convoluted tubule filtrate reabsorption

remains relatively constant

the distal convoluted tubule filtrate reabosorption

is tightly regulated, can quickly change depending on body conditions

renin-angiotensin-aldosterone system

a hormone cascade pathway that helps regulate blood pressure and blood volume

When is RAAS (renin-angiotensin-aldosterone-system) activated?

initiated under low blood pressure conditions

where is renin secreted from

juxtaglomerular cells

renin converts into

angiotensinogen into angiotensin I