session 11 + 12

what are functions of the kidney

• Urine formation

• Urine transport

• Urine storage and release

• Regulates blood pressure

• Stimulates erythropoiesis

• Activation of Vit D

• pH control

what are the structural and functional units that form urine

nephron

what are the two main parts of the nephron

1. Glomerulus: a tuft of capillaries

2. Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus

what is the proximal convoluted tubule

– Cuboidal cells with dense microvilli and large mitochondria

– Functions in reabsorption and secretion

– Confined to the cortex

what is the loop of henle

• Simple squamous epithelium

• Freely permeable to water (but not in thick ascending limb)

what is the distal convoluted tube

– Function more in secretion than reabsorption

what are the collecting ducts

• Receive filtrate from many nephrons

• Fuse together to deliver urine through papillae into minor calyces

what are the 3 phases of urine formation

 Glomerular filtration

 Tubular reabsorption

 Tubular secretion (Elements from blood to )

what occurs in glomerular filtration

• Principles of fluid dynamics that account for tissue fluid in all capillary beds apply to the glomerulus as well

• The glomerulus is more efficient than other capillary beds because:

– Its filtration membrane is significantly more permeable

– Glomerular blood pressure is higher

– It has a higher net filtration pressure

• Plasma proteins are not filtered and are used to maintain oncotic pressure of the blood

what are the forces of glomerular filtration

– Glomerular hydrostatic pressure (HPg) [Blood  capsule]

– Glomerular oncotic pressure = osmotic flow toward blood;

» [Capsule  blood]

– Bowman’s capsule pressure= pressure exerted by capsular fluid

» [Capsule  blood]

Net filtration pressure (NFP)

what is the function of bowman’s capsule

to catch and collect fluid and waste squeezed out of the blood during the first step of kidney filtration

why is the efferent arteriole smaller than the afferent arteriole

to create more pressure for exiting materials

net filtration pressure =

glomerular hydrostatic pressure - bowman’s capsule pressure - glomerular oncotic pressure

what is the functional unit of the kidney

nephron

how many nephrons are in the kidney

around one million

is glomerular filtration into the kidney or excreted

excreted

is tubular reabsorption into the kidney or excreted

into the kidney

is tubular secretion into the kidney or excreted

excreted

if glomerular filtration rate is too high:

useful substances are lost due to the speed of fluid passage through nephron

if glomerular filtration rate is too low:

waste products may not be removed from the body

filtration stops if net filtration pressure is less than or equal to:

0

filtration functions normally with mean arterial pressures ______

80-180 mmHg

the early proximal tubules reabsorb:

• all of the glucose and amino acids

• Most of the bicarbonate, Na+, Cl-, and H2O by isotonic absorption.

• Phosphate

the early proximal tubules secretes:

• Ammonia, uric acid, organic acid

• Creatinine (increased creatinine level in blood is a marker for kidney malfunction)

what hormones affect early proximal tubules

• PHT: parathyroid hormone; decrease PO43- reabsorption

• AT II: angiotensin II; increase Na+ and H2O reabsorption to increase blood pressure (increased blood volume)

without the loop of henle:

urine would always be the same concentration as blood, and we would lose too much water

what occurs in the descending limb

water leaves but salts stay, so the fluid becomes more concentrated.

what occurs in the ascending limb

salts are pumped out but water stays in, so the fluid becomes more dilute

Dilute urine is made when the body has _____ water, such as after drinking a lot.

extra

Concentrated urine is made when the body needs to save water, such as in ___________

dehydration

is the descending loop water permeable

yes

is the ascending loop water permeable

no

what does the descending loop of henle reabsorb

• H2O only

• Do not absorb salt

• Concentrating segment

• Makes urine hypertonic

what does the ascending loop of henle reabsorb

• Na+, K+, and Cl- by active reabsorption

• Indirectly induces Mg2+ and Ca2+ reabsorption

• NOT permeable to H2O

• Makes urine less concentrated

In the descending limb, ____ leaves but _____ stay, so the fluid becomes more ________.

water; salts; concentrated

In the ascending limb, ____ are pumped out but _____ stays in, so the fluid becomes more _____.

salts; water; dilute

what does the distal convoluted tubule reabsorb

• Actively reabsorb Na+, Cl-

• Diluting segment

• Makes urine more hypotonic

what does the distal convoluted tubule secrete

K+ and H+

what hormones are involved in the distal convoluted tubule

PHT: parathyroid hormone; increase Ca2+/Na+ exchange; Ca2+ reabsorption

what do the collecting tubules reabsorb

Na+

what do the collecting tubules secretes

H+ and K+

what is the function of aldosterone

leads to insertion of Na+ channel on luminal side; Na+/H2O retention; blood volume increase; blood pressure increase

what is the function ADH

increase H2O permeability; less urine excretion

makes the collecting ducts more permeable to water, increasing water reabsorption and concentrating urine

what does a deficiency of ADH cause

(Diabetes Insipidus) Kidneys can’t reabsorb water → patients pass huge volumes of dilute urine, intense thirst.

what is the function of PTH

increases calcium reabsorption and decreases phosphate reabsorption.

what is the function of atrial natriuretic peptide (ANP)

increases sodium and water excretion by dilating the afferent arteriole, raising GFR, and reducing sodium reabsorption

what is the clinical relevance of heart failure

ANP resistance

Even though ANP levels are high, the kidneys may not respond effectively → fluid retention, edema, and worsening heart failure

what secretes renin

kidney

what does renin act on

angiotensinogen (gamma globulin from the liver) giving angiotensin I

what does angiotensin converting enzyme (ACE) act on

angiotensin I giving angiotensin II

what is the function of renin

1. Changes in secretion is in response to changes in renal arterial pressure, sympathetic nervous system signals and some hormones

2. Its substrate is angiotensinogen

what is angiotensinogen

It is a glycoprotein synthesized and secreted into the bloodstream by the liver

what is the function of ACE

It converts angiotensin I to II (vasoconstrictor) and inactivates bradykinin (vasodilator)

what is the principal site of action of ACE

vascular epithelium

what is ACE inhibited by

synthetically produced Captopril drug

what is the role of angiotensin II

• powerful vasoconstrictor. It constricts the blood vessels and raises the peripheral resistance, thereby acting to restore blood pressure.

• Angiotensin ll also increases the secretion of aldosterone leading to Na+ reabsorption

what is abnormal renal function if protein is present

Protein present → kidney damage (proteinuria)

what is abnormal renal function if glucose is present

uncontrolled diabetes or tubular problem

what is abnormal renal function if blood is present

stones, infection, or glomerular disease

what is abnormal renal function if ketones is present

diabetes or starvation

what is abnormal renal function if too many white blood cells are present

infection or inflammation

what are the major markers for kidney function in the blood

Creatinine, BUN, eGFR, Glucose

what are the major markers for kidney function in the urine

Protein, Blood, Glucose, WBCs, RBCs

what does high creatine in blood work mean

poor kidney filtration

what does high blood urea nitrogen (BUN) in blood work mean

kidney impairment or dehydration

what does low GFR in blood work mean

reduced kidney function (CKD or failure)

what does high glucose in blood work mean

diabetes, risk for kidney damage