BIO TEST #9 - URINARY SYSTEM

the urinary system is involved in excretion, which is what?

removal of metabolic wastes from the body

what does the urinary system produce and then conducts it to outside the body?

urine

as the kidneys produce urine, what four functions do they carry out that contribute to homeostasis

excretion of metabolic waste, osmoregulation, regulation of acid-base balance, and secretion of hormone

excretion of metabolic wastes: what excretes metabolic wastes and what does metabolic waste consist of

kidneys excrete metabolic wastes which are most nitrogenous wastes like urea, ammonium, creatinine, and uric acid

excretion of metabolic wastes: urea is a by-produce of amino acid metabolism. how is urea formed?

when ammonia is released by the liver during amino acid breakdown combines with CO2

excretion of metabolic wastes: ammonia is very toxic to cells but urea is much less toxic. how are some ammonia (NH3) excreted as?

ammonium ions (NH4+)

excretion of metabolic wastes: what is creatinine

a breakdown product of creatine phosphate, a high-energy phosphate reserve molecule

excretion of metabolic wastes: what produces uric acid? (insoluble)

the breakdown of nucleotides

excretion of metabolic wastes: what is gout?

can occur if too much uric acid in the blood has crystalized and moved into the joints

Osmoregulation: the kidneys are involved in osmoregulation. what is osmoregulation?

maintenance of the balance of water and salt in the blood

Osmoregulation: how does the amount of salt in our body directly control blood volume and blood pressure? aka how are the kidneys involved with blood pressure

salt can cause osmosis (diffusion of water) into the blood. the more salts there are in the blood, the greater the blood volume and blood pressure

Osmoregulation: what ions do the kidneys help maintain?

potassium (K+), bicarbonate (HCO3-) and calcium (Ca2+) in the blood

regulation of Acid-Base Balance: along with the respiratory system, how do the kidneys regulate the acid-base balance

they monitor and keep the blood pH at 7.4 by excreting hydrogen ions and reabsorbing the bicarbonate ions

what is the pH of human urine?

6

secretion of hormones: how do the kidneys assist the endocrine system in hormone secretion?

they release renin, an enzyme that stimulates the adrenal cortex to secrete the hormone aldosterone which promotes the absorption of sodium ions by the kidneys

secretion of hormones: what other hormone do the kidneys secrete

erythropoietin (EPO) to stimulate red blood cell production when oxygen demands increases

secretion of hormones: what do the kidneys have to do with vitamin D and what is vitamin D

helps activate it from the skin. it is a hormone-like molecule that promotes calcium absorption from the digestive tract

what does the urinary system consist of

kidneys, ureters, urinary bladder, and urethra

describe the location and general shape of the kidneys

paired, bean-shaped organs located near the small of the back in depressions

what covers each kidney?

a tough fibrous connective tissue layer called a renal capsule

describe the concave side of each kidney

has a depression called a hilum where a renal artery enters and a renal vein and ureter exit

what conducts urine from the kidneys to the bladder?

ureters

describe ureters

small muscular tubes that descend from the hilum of the kidney to the bladder

describe the wall of a ureter

three layers; inner mucosa, smooth muscle layer, and an outer fibrous coat of connective tissue

what causes urine to enter the bladder?

peristaltic contractions in the ureter

a healthy human produces 1-2L of urine a day, how much of that enters the bladder per hour?

40-80mL

what stores urine until it is expelled from the body

urinary bladder located in the pelvic cavity

describe the openings of the urinary bladder?

three openings, two for the ureters and one for the urethra which drains the bladder

how is the bladder wall expandable?

it contains a middle layer of circular fibre and two layers of longitudinal muscle as well as transitional epithelium of the mucosa which becomes thinner and the folds called rugae disappear

what prevents the backflow of urine after it enters the bladder

small folds of bladder mucosa that act like a valve

what lies close to where the urethra exits the bladder?

two sphincters; an internal one that occurs around the opening to the urethra and an external one made of skeletal muscle that can be voluntarily controlled

what is incontinence

involuntary loss of urine, occurs in older people from the loss of muscle tone and during pregnancy/nervous system diseases

what is the small tube opening that extends from the urinary bladder to a external opening?

urethra which removes urine from the body

describe the difference in urethra in men/woman

in men, the urethra is about 20cm long carrying both urine and semen, and in women, it is about 4cm long only carrying urine

in which gender would you find a urinary bladder encircled by a prostate gland? making them a target for prostate cancer and prostate enlargement which can restrict urination

men

what happens when the bladder fills to about 250mL

stretch receptors send sensory nerve impulses to the spinal cord then motor nerve impulses from the spinal cord causes the bladder to contract and the sphincters to relax, causing urination

many branches of the renal artery and renal vein reach inside the kidney. what are the three regions of the kidney?

renal cortex, renal medulla, and renal pelvis

what is the renal cortex

outer, granulated layer

what is the renal medulla

contains cone shaped tissue masses called renal pyramids

what is the renal pelvis

central space that is continuous with the ureter

the kidney is composed of over 1 million what?

nephrons, also known as renal or kidney tubules

each nephron has its own blood supply including two capillary regions. how is the renal artery involved with nephrons?

from the renal artery, an afferent arteriole leads to the glomerulus

what is a glomerulus

a knot of capillaries inside the glomerular capsule

what happens to the blood leaving the glomerulus?

it enters the efferent arteriole which takes blood to the peritubular capillary network which surrounds the rest of the nephron before exiting through a venule and into the renal vein

describe the glomerular capsule (bowmans capsule)

inner layer composed of podocytes that have long cytoplasmic extensions

what do the podocytes in the glomerular capsule do?

they cling to capillary walls of the glomerulus and leave pores small molecules from the glomerulus to enter the capsule

what does the glomerular capsule connect to

proximal convoluted tubule (PCT)

what lines the proximal convoluted tubule

cuboidal epithelial cells that have packed microvilli to increase the surface area for reabsorption and several mitochondria to carry out active reabsorption of substances

what does the proximal convoluted tubule lead into

it narrows and makes a U turn called the loop of Henle or loop of the nephron

describe the loop of henle

consists of a descending limb and an ascending limb and is lined with simple squamous epithelium

following the loop of henle, the tube becomes what?

the distal convoluted tubule

what is the distal convoluted tubule composed of

cuboidal epithelial cells that lack microvilli but have many mitochondria

what does the lack of microvilli in the distal convoluted tubule mean

it helps move molecules from the blood into the tubule, a process called tubular secretion

what does the distal convoluted tubule of several nephrons enter

one collecting duct which carry urine to the renal pelvis

which part of the kidney does the glomerular capsule and convoluted tubules lie within

renal cortex

which part of the kidney does the loop of henle and collecting ducts dip down into

renal medulla

urine formation is divided into which following processes

pressure filtration, selective reabsorption, and tubular excretion

when does pressure filtration occur?

when blood enters the afferent arteriole and the glomerulus

what happens with pressure filtration?

due to glomerular blood pressure, water, salts, nutrients, and wastes (glomerular filtrate) move from the glomerulus to the inside of the glomerular capsule

what cannot pass into the capsule

large molecules and formed elements cannot pass through the capillary wall

how many litres of water do the nephrons in the kidneys filter each day

180L

why must the composition of the glomerular filtrate be altered as it passes through the kidney tubules?

because if urine has the same concentration as filtrate, the body would lose vital water, salts, and nutrients

what happens in selective reabsorption

nutrients and ions from the glomerular filtrate in the tubules are passively and actively reabsorbed into the blood of the peritubular capillary network

how is the osmolarity of the blood maintained?

presence of both plasma proteins and salts

what happens when Na+ ions are actively reabsorbed

chloride ions follow passively and the reabsorption of salt (NaCl) increases the osmolarity of the blood compared to the filtrate, resulting in water moving passively from the tubule into the blood

what percent of sodium (Na+) is reabsorbed at the proximal convoluted tubule

65%

besides salts and water, what else gets reabsorbed

glucose and amino acids are actively reabsorbed into the blood at the proximal convoluted tubule

what is a example of a molecule that ordinarily is completely reabsorbed

glucose because there is a lot of carrier proteins for it

every substance has a maximum rate of transport, what does this mean?

after all its carriers are in use, any excess in the filtrate will appear in the urine

in diabetes mellitus, excess glucose appears in the blood, because the liver and muscles failed to store glucose as glycogen. how does this affect the urinary system

kidneys cannot reabsorb all the glucose in the filtrate which increases the filtrates osmolarity so less water is reabsorbed into the capillary network and it appears in the urine

what are the reabsorbed filtrate components

most water, nutrients, and required salts (ions)

what are the nonreabsorbed filtrate components

some water, most nitrogenous waste, excess salts (ions)

what do the substances that are not reabsorbed become?

tubular fluid which enters the loop of henle

what is tubular excretion

another way substances are removed from blood in the peritubular capillary network and added to the tubular fluid

what are some examples of substances that are removed by active transport from the blood in the peritubular capillary network into the convoluted tubules

hydrogen ions, potassium ions, creatinine, and drugs like penicillin

in the end, what does urine contain

substances that have undergone glomerular filtration but have not been reabsorbed and substances that have undergone tubular excretion

where is most of the water and salt (NaCl) present in the filtrate reabsorbed?

across the wall of the proximal convoluted tubule

how do the kidneys maintain blood volume and blood pressure

they maintain the water-salt balance in the blood through osmregulation

what is the excretion of urine that is more concentrated than blood dependent on

hypertonic urine depends on the reabsorption of water from the loop of Henle and the collecting duct

what does the reabsorption of water require

reabsorption of salt, establishment of a solute gradient dependent on salt and urea before, and water reabsorption

during the process of reabsorption, water passes through which water channels?

aquaporins which are proteins embedded in the plasma membrane

how do the kidneys regulate salt balance

by controlling the excretion and reabsorption of various ions (ie sodium)

sodium (Na+) is an important ion in plasma that must be regulated, but what else do the kidneys excrete or reabsorb?

potassium ions, bicarbonate ions, and magnesium ions

how does more than 99% of sodium filtered at the glomerulus get returned into the blood

67% is reabsorbed at the proximal convoluted tubule, 25% is reabsorbed by the ascending limb and the rest is reabsorbed from the distal convoluted tubule

which hormones regulate the reabsorption of Na+ at the distal convoluted tubule?

aldosterone and atrial natriuretic hormone (ANH)

describe aldosterone

hormone excreted by the adrenal cortex (kidneys) that promotes the excretion of K+ and the reabsorption of Na+

what is the juxtaglomerular apparatus

region of contact between the afferent arteriole and the distal convoluted tubule

what does the juxtaglomerular apparatus do?

when blood volume/pressure is not sufficient to promote glomerular filtration, it secretes the enzyme renin

what does renin do

changes angiotensinogen into angiotensin I which converts into angiotensin II that stimulated the adrenal cortex to release aldosterone

aldosterone promotes the reabsorption of Na+ which leads to reabsorption of water and therefore?

blood volume and blood pressure increase