Urinary system Flashcards
Name the three functions of the urinary system
- Urine excretion
- Endocrine organ
- Homeostatic role (controls blood pressure, tissue osmolality, electrolyte and water balance and plasma pH
How can the kidneys affect the pH balance?
- Excreting hydrogen ions in acidosis and bicarbonate ions in alkalosis
How can the kidneys indirectly raise the blood pressure and drive red blood cell production?
- They secrete renin which raises blood pressure
- They secret erythropoietin which drives red blood cell production
What carries urine from the kidneys to bladder?
- Ureters
Describe the position of the kidneys
- They are high up in the abdomen with one on each side.
- They sit inferior to the diaphragm and posterior to the abdominal wall in the retroperitoneal space
What protects the kidneys?
- They are encapsulated by layers of fascia and firm renal fat
Describe the basic internal structure of the kidney
- The outer portion of the kidney is called the cortex
- The cortex extends down between medullary pyramids
- The pyramids project into a minor calyx (calyces for plural)
- The minor calyces converge into major calyces, which form the renal pelvis at the hilum
- The renal pelvis becomes the ureter
What is the functional unit of the kidney?
Where are they located?
- The functional unit of the kidney is called a nephron
- Nephrons are found in the medullary pyramids
Describe the basic structure of a nephron?
- The renal corpuscle (glomerulus) is in the bowman’s capsule, and is where the blood supply comes in
- Then it moves into the proximal convoluted tubule
- Then into The loop of Henle, which is closely related to circulation, and is important when determining the concentration of urine.
- This then moves into the distal convoluted tubule which them moves into a collecting duct (where a number of nephrons merge together).
How does the structure of the collecting duct change?
- It increases in size
Name the two different types of nephrons and describe them
Juxtamedullary nephron -
- Located in the inner cortex
- This is designed to concentrate and dilute urine
- They have long nephron loops
The superficial nephron -
- Located in outer cortex
- They reabsorb a large volume of fluid that is filtered from vasculature
- Short nephron loops
Describe the general location of the ureter in females
- Females - posterior to ovary, lateral to cervix and anterior to the womb
Describe the general location of the ureter in men
- Superior to the bladder.
Describe the basic structure of the ureter
How does it propel urine downwards?
How does it stop urine from refluxing?
- It is muscular and uses peristaltic waves to propel urine downwards
- It also contains a one-way valve to prevent urine reflux into the ureter once in the bladder
What is the bladder made from?
How is the bladder filled?
How is the bladder emptied?
What is the bladder lined by?
- It is made of smooth muscle
- It is filled by relaxation of its muscular wall (the detrusor muscle)
- It is emptied by the contraction of the detrusor muscle, which is aided by raising intra-abdominal pressure.
- Lines by urothelium (transition epithelium)
Where does the filtration process occur?
How does it occur?
What are starlings forces?
Why allows/prevents small/large molecules moving into the bowman’s capsule.
- Blood enters the glomerulus in the bowman’s capsule, where it is filtered
- There is net flow out of filtrate in the glomerulus to the bowman’s capsule, as the hydrostatic pressure is higher than the oncotic pressure in the capillaries of the glomeruli.
- The hydrostatic and oncotic pressure are referred to as Starling’s forces
- The glomerular capillaries have endothelial cells which are fenestrated
- There is a basement membrane, then filtration slits between podocytes
- These filtration slits and fenestrated capillaries allow small molecules, such as glucose, to move out into the bowman’s capsule, while large molecules are kept in the blood.
What is osmolality?
How does osmolality change at different parts of the kidney?
- Osmolality refers to the concentration of dissolved particles, such as sodium and electrolytes, present.
- It ranges from relatively low osmolality from the cortex and outer medulla to high osmolality in the inner medulla (where the loops of henle are located)
Give an overview of the reabsorption process.
- Sodium/potassium ATPase creates a sodium gradient and provides energy for transportation.
- Ion transport creates a voltage gradient between the nephron tubule lumen and interstitium of the nephron
- This allows for more movement of substances across the membrane to be reabsorbed into peritubular circulation
- Water follows sodium and is reabsorbed by osmosis.
- Solvent drag means solutes are carried along in the water flow.
- A concentration of solutes is left in the lumen after water reabsorption.
Describe how water is reabsorbed as it moves through the proximal convoluted tubule of the nephron
- As filtrate comes down from the proximal convoluted tubule, water is exposed to high osmolality, and is driven out due to the osmotic pressure gradient.
What prevents water from being absorbed in the nephron?
Why is this the case?
- The impermeability of the ascending limb of the loop prevents water from re-entering and diluting its contents.
- Dilution would collapse the gradient that drives sodium diffusion out of the nephron (generated by Na/K ATPase)
What is the type of epithelium that lines the proximal convoluted tubules?
What 2 features does it have and why?
What is the epithelium in the lumen of the loops of henle?
What is the epithelium in the lumen of the distal convoluted tubules?
- it is simple cuboidal epithelium
- They have apical microvilli, which increases surface area
- The tight junctions between cells are leaky, so they maximise free flow of water and dissolved solutes
- the loops of henle contain simple squamous epithelium.
- the distal convoluted tube contains simple cuboidal epithelium, with few microvilli
What controls the outflow of urine via the urethra
what are they controlled by?
- Inner and outer sphincters control outflow of the urine from the urethra
- The inner sphincter and bladder contraction is controlled by spinal reflexes and the CNS.
- The outer sphincter is under voluntary control.
What does filling of the bladder cause?
- Urine filling the bladder causes the muscular wall to stretch, which initiates a spinal micturition reflex.
- This reflex causes the parasympathetic motor efferents to stimulate bladder contraction
What prevents you from urinating?
- The central nervous system prevents urination.
- The bladder will only empty when the outer sphincter is voluntarily relaxed
