Urinary system Flashcards
What are the functions of the urinary system?
Regulate the blood volume and composition.
Regulate Blood Pressure
Storage as well as excretion of waste product via urine
what are the main functions of the kidneys?
Formation of urine, maintaining water, electrolyte and acid-base balance
excretion of waste products
production and secretion of erythropoietin, the hormone which stimulates formation of red blood cells
Where do the kidneys lie?
on the posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum and below the diaphragm.
Extend from the level of the 12th Thoracic vertebra to the 3rd lumbar vertebra.
The right kidney is normally slightly lower than the left, due to the space occupied by the liver.
What are the different tissue layers of the kidney?
An outer, fibrous capsule, surrounding the kidney.
The cortex, a reddish-brown layer of tissue immediately below the capsule and surrounding the renal pyramids.
The medulla, the innermost layer, consisting of pale, conical-shaped, striated structures, the renal pyramids. Each pyramid has a pointed end called the papilla.
What is the hilum of the kidney?
The concave medial border of the kidney, where the renal blood and lymph vessels, the ureter and the nerves enter.
How does urine exit the kidneys?
It passes through a renal papilla into the drainage system that begins at a minor calyx, several of which will merge into a major calyx, and again, several will combine forming the renal pelvis.
The renal pelvis is a hollow funnel-shaped structure that narrows when it leaves the kidney as the ureter. The ureter leads to the bladder.
What are the walls of the calyces and renal pelvis lined with?
Transitional epithelium and contains smooth muscle.
How is urine propelled through the calyces, renal pelvis and ureters?
Peristalsis, the intrinsic contraction of smooth muscle.
What do nephrons consist of?
Glomerular capsule (bowman’s capsule) which almost completely encapsules a bundle of capillaries called the
Glomerulus
Proximal convoluted tubule
The medullary loop (loop of Henle)
Distal convoluted tubule leading to the
collecting duct
The collecting ducts merge, forming larger ducts which empty into the minor calyces.
How does blood flow around the kidneys?
The renal artery enters the kidney at the hilum. It then divides into smaller arteries and arterioles.
An afferent arteriole enters each glomerular capsule and then subdivides into a cluster of tiny arterial capillaries, forming the glomerulus. The blood vessel leading away from the glomerulus is the efferent arteriole.
What drives filtration in the nephrons?
The afferent arteriole has a larger diameter than the efferent arteriole, increasing the pressure inside the glomerulus and drives filtration across the glomerular capillary walls.
What are the walls of the glomerulus and glomerular capsule made of?
What are the walls of the rest of the nephron made of?
A single layer of flattened epithelial cells. They are very permeable to facilitate filtration.
The walls of the remainder of the nephron and the collecting duct are formed by a single layer of simple squamous epithelium.
What are the 3 processes in the formation of urine?
Filtration, selective reabsorption, secretion
Where does filtration take place?
What happens?
The semipermeable walls of the glomerulus and the glomerular capsule.
Water and other small molecules readily pass through, although some are reabsorbed later. Blood cells, plasma proteins and other large molecules are too large to filter through and therefore remain in the capillaries.
What is the glomerular filtration rate?
the volume of filtrate formed by both kidneys each minute. In a healthy adult, it’s about 125ml/min.
Nearly all filtrate from the kidneys is reabsorbed, with less than 1% excreted as urine.
What is autoregulation?
The mechanism protecting renal blood flow from fluctuations in blood pressure.
This system fails when systolic blood pressure falls below 80mmHg.
Where does most selective reabsorption take place?
Proximal convoluted duct. The epithelial lining of which possesses microvilli to aid reabsorption. Water, electrolytes, glucose and amino acids are reabsorbed here.
Which hormones influence calcium reabsorption?
Parathyroid hormone - regulates the reabsorption of calcium and phosphate so that normal blood levels are maintained. Parathyroid hormone increases blood calcium levels and calcitonin lowers it.
Which hormone influences water reabsorption?
Antidiuretic hormone increases the permeability of the distal convoluted tubule, increasing water reabsorption. Osmoreceptors in the hypothalamus monitor water levels in the blood and ADH secretion is adjusted accordingly.
What does aldosterone do?
Secreted by the adrenal cortex, it increases the reabsorption of sodium and water, and the excretion of potassium.
Which hormone decreases reabsorption of sodium and water?
Atrial natriuretic hormone is produced by the atria of the heart in response to stretching of the atrial wall when blood volume is increased.
What is tubular secretion?
Substances that have not been entirely filtered out of the blood due to size or the short time they remain in the glomerulus are secreted into the filtrate within convoluted tubules. The secretion of hydrogen ions is important in maintaining normal blood ph.
Why is urine amber in colour?
Due to the presence of urobilin.
What is excreted in urine?
water (95%)
urea (2%)
uric acid
creatinine
ammonia
sodium
potassium
chlorides
phosphates
sulphates
oxalates
