AAP Urinary System 2 Flashcards
1
Q
What are the main functions of kidneys?
A
- excretion of wastes and toxins
- regulation of extracellular fluid volume to ensure an adequate blood supply to vital organs
- regulation of osmolarity
- regulation of ion concentrations (pH)
- production of hormones (Erythropoietin, EPO, –> stimulates bone marrow for RBC production
2
Q
What are the three main steps of urine formation?
A
- glomerular filtration
- tubular reabsorption
- tubular secretion
3
Q
What happens during urine formation?
A
- the kidneys filter unwanted substances from the blood and produce urine to excrete them
4
Q
How is glomerular filtrate formed?
A
high blood pressure in the glomerular capillaries forces some plasma out of the capillaries and into the capsular space of Bowman’s capsule
5
Q
Describe the structure of the glomerular capillaries.
A
- contain many large openings, known as fenestrations, in the capillary endothelium
- fenestrations are not large enough to allow blood cells or large proteins to pass through
6
Q
Describe glomerular filtration.
A
- glomerular capillaries contain many large openings, known as fenestrations, in the capillary endothelium
- fenestrations are not large enough to allow blood cells or large proteins to pass through
- it facilitates more fluid to leave the bloodstream
- glomerular filtrate is similar to plasma except that it contains no proteins
- the speed of filtration is determined by the glomerular filtration rate (GFR)
- high blood pressure in the glomerular capillaries forces some plasma out of the capillaries and into the capsular space of the Bowman’s capsule, and becomes glomerular filtrate.
7
Q
What is the purpose of kidney reabsorption?
A
- ensures the body gets back the small useful molecules from the filtrate (in the tubule)
8
Q
What happens during kidney reabsorption?
A
- substances to be reabsorbed pass through the tubular lumen
- and enter interstitial fluid (in tissue space –> interstitial space)
- and then pass through tubular wall and capillary wall into the blood circulation
- this is achieved by either passive diffusion and/or active transport
- 65% of reabsorption takes place in the PCT, the remaining reabsoption takes place in the DCT and LOH
- 80% of water, sodium, chloride, and bicarbonate is reabsorbed
- 100% of the glucose and amino acids are reabsorbed
9
Q
Sodium reabsorption
A
- sodium can be reabsorbed by active transport, where transporter protein carry sodium through epithelial cell in the PCT
- sodium ions are also reabsorbed in the LOH and DCT (as exchange for hydrogen, ammonium, or potassium ions)
10
Q
Glucose and amino acid reabsorption
A
- glucose and amino acids are transported and absorbed by similar process as sodium in the PTC
11
Q
Potassium and calcium reabsorption
A
- takes place mainly in the PCT
- most of the potassium and calcium are reabsorbed by passive diffusion
- reabsorption of calcium is modulated by vitamin D, parathyroid hormone (PTH) and calcitonin (by thyroid)
12
Q
Chloride reabsorption
A
- chloride diffuses through in response to electrical imbalance created by absorption of (Na+)
- chloride moves by following the movement of sodium
- water is absorbed by following osmosis once sodium, glucose, amino acids and chloride have left the tubular filtrate, water molecules follows
13
Q
What is secretion?
A
- the process by which the substances move into tubules (urine) from blood capillaries
- many substances that are not filtered from blood are eliminated by this process
(such as extra amt of hydrogen, potassium, ammonia, urea, certain drugs and other wastes) - occurs in PCT, LOH, DCT
14
Q
What hormones control the urine volume regulation?
A
- antidiuretic hormone (ADH) from pituitary gland
- aldosterone from adrenal cortex
15
Q
What do ADH and aldosterone do?
A
- ADH acts on the DCT (and CT) to promote water reabsorption back into blood
- aldosterone acts on the DCT to increase reabsorption of sodium
- causes osmotic imbalance that encourages water to follow sodium back into the blood
16
Q
What is renin?
A
- hormone secreted in the glomerulus in response to low arterial pressure
- converts angiotensinogen (serum protein produced in the liver) to angiotensin
17
Q
What does angiotensin do?
A
- causes vasoconstriction and stimulates the release of aldosterone (from adrenal cortex of the kidney
18
Q
Process to increase sodium reabsorption at DCT.
A
- renin is secreted in the glomerulus in response to low arterial pressure
- renin converts angiotensinogen to angiotensin
- angiotensin causes vasoconstriction and stimulates the release of aldosterone
- the release of aldosterone from the adrenal cortex leads to an increase in sodium reabsorption at DCT
19
Q
What are baroreceptors?
A
- pressure sensors in the blood vessels
- sense the change of blood pressure and relay the information to the brain to modulate blood pressure (by changing cardiac output and vascular smooth muscle)
20
Q
What are osmoreceptors?
A
- found in the hypothalamus
- sense the change of the blood osmotic pressure
- modulate the secretion of ADH
21
Q
Diabetes insipidus
A
- insufficient production of ADH by pituitary gland results in reduced water absorption by the kidney and consequently a large volume of diluted urine
- frequent urination (polyuria)
- frequent drinking of water (polydipsia) due to thirst
22
Q
Diabetes mellitus
A
- commonly known as diabetes
- due to the increased blood glucose level from insufficient insulin
- similar symptoms as diabetes insipidus (polyuria and polydipsia)
23
Q
Structure of ureters
A
- outer fibrous layer
- middle smooth muscle layer
- inner layer lined with transitional epithelium
24
Q
How does the structure of ureters help with its function?
A
- transitional epithelium allows ureters to stretch as urine passes through
- middle smooth muscle layer propels urine through the ureters by peristaltic contractions
25
Ureters to urinary bladder
- ureters enter the urinary bladder at an oblique angle
- forms a functional valve to prevent backflow into ureter
- when the bladder is full, urine presses the entrance to close it
When the bladder is empty, the entrance is open to receive the urine from the ureter
26
Structure of urinary bladder
- lined with transitional epithelium that stretches as the bladder is filled with urine
- the wall of the urinary bladder contains smooth muscle (known as detrusor muscle)
- around the neck of the urinary bladder are circular muscles (sphincter muscles)
27
Sphincter muscles (internal and external sphincter muscles)
- internal sphincter muscle: smooth muscle under involuntary control
- external sphincter muscle: skeletal muscle under voluntary control --> allows voluntary control of urination
28
Urethra
- continuation of the neck of the urinary bladder
- carries urine from the bladder to the external environment
- lined with transitional epithelium which allows it to expand
- the female urethra is shorter and straighter compared to the long, curved urethra in male
- in the female, the urethra opens on the ventral portion of the vestibule of the vulva --> only serves as urinary function
- in the male, the urethra runs down the centre of the penis and also functions to carry semen
29
Control of urination process
- urination is the excretion of urine from the urinary bladder into the urethra
- building up pressure in bladder activates stretch receptors (pressure sensor) in bladder wall
- which activates a spinal reflex that cause bladder smoother muscles to contract
- contraction give sensation of having to urinate
- voluntary control of the external sphincter around the neck of the bladder allows the temporary control of urination
- house-trained animals can exercise voluntary control of the external sphincter muscle to temporarily hold the urine
- beyond a certain pressure limit, the sphincter eventually relaxes to release the urine
