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uitgebreide Samenvatting hoofdstuk 19 silverthorn human physiology
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Fleur sam Ch. 1919.1 functions of the kidneys
Urine, the fluid waste produced by the kidneys, reflects the functioning of the body.
The first step in examining a urine sample is to determine its color.
Its dark yellow (concentrated), pale straw (dilute), red (indicating he presence of
blood), black (indicating the presence of hemoglobin metabolites).
One form of malaria was called blackwater fever bc metabolized hemoglobin from the
abnormal breakdown of RBCs turned victim’s urine black or dark red.
Physicians also inspected urine samples for clarity, froth (incating abnormal presence
of proteins), smell, and taste.
Diabetes is endocrine disorder characterized by the presence of glucose in the urine,
diagnosis: honey-urine disease.
Nowadays, more sophisticated tests for glucose in urine, first step is always
urinalysis, to examine the color, clarity and odor of the urine.
Most important function of kidney is the homeostatic regulation of the water and ion
content of the blood, also called salt and water balance or fluid and electrolyte
balance.
Waste removal is important, but disturbances in blood volume or ion levels cause
serious medical problems before the accumulation of metabolic wastes reaches toxic
levels.
The kidneys maintain normal blood conc. of ions and water by balancing intake of
those substances with their excretion in the urine, obeying the principle of mass
balance.
Kidney function can be divided into 6 general areas:
1. Regulation of ECF volume and blood pressure. When ECF volume decreases,
blood pressure also decreases. If ECF volume and blood pressure fall too low, the
body cannot maintain adequate blood flow to the brain and other essential organs.
The kidneys work in an integrated fashion with the cardiovascular system to ensure
that blood pressure and tissue perfusion remain within an acceptable range.
2. Regulation of osmolarity. The body integrates kidney function with behavioural
drives, like thirst, to maintain blood osmolarity at a value close to 290 mOsM.
3. Maintenance of ion balance. The kidneys keep conc. of key ions within a normal
range by balancing dietary intake with urinary loss. Sodium (Na+) is the major ion
involved in the regulation of ECF volume and osmolarity. Potassium (K+) and calcium
(Ca2+) conc. are also closely regulated.
4. Homeostatic regulation of pH. The pH of plasma is normally kept within a narrow
range. If ECF becomes too acidic, the kidneys remove H+ and conserve bicarbonate
ions (HCO3-) which act as a buffer. When ECF becomes too alkaline, the kidneys
remove HCO3- and conserve H+. the kidneys play significant role in pH homeostasis,
but they do not correct pH disturbances as rapidly as the lungs do.
, 5. Excretion of wastes. The kidneys remove metabolic waste products and
xenobiotics, or foreign substances, like drugs and environmental toxins. Metabolic
wastes include creatinine from muscle metabolism and the nitrogenous wastes urea
and uric acid.
A metabolite of hemoglobin called urobilinogen gives urine its characteristic yellow
color.
Hormones are another endogenous substance the kidneys clear from the blood. Bv.
of foreign substances that kidneys actively remove include the artificial sweetener
saccharin and the anion benzoate, part of the preservative potassium benzoate,
which are in diet soft drinks.
6. Production of hormones. Although the kidneys are not endocrine glands, they
play important roles in 3 endocrine pathways:
- Kidney cells synthesize erythropoietin, the cytokine/hormone that regulates RBC
synthesis.
- They also release renin, an enzyme that regulates the production of hormones
involved in sodium balance and blood pressure homeostasis.
- Renal enzymes help convert vitamin D3 into a hormone that regulates Ca2+
balance.
The kidneys, like many other organs have tremendous reserve capacity. By most
estimates, you must lose nearly 3/4th of your kidney function before homeostasis
begins to be affected. Many people function perfectly normal with only 1 kidney.
(1/1000 people are born with 1 kidney, bc other kidney fails to develop during
gestation) or people who donate a kidney for transplantation.
19.2 anatomy of the urinary system
The urinary system is composed of kidneys and accessory structures. The study of
kidney function is called renal physiology (renes=kidneys).
Urine production begins when water and solutes move from the plasma into the
hollow tubules, = nephrons that make up the bulk of the paired kidneys.
These tubules modify the composition of the fluid as it passes through. The modified
fluid, now called urine, leaves the kidney and passes into a smooth muscle tube
called a ureter. There are 2 ureters, one leading from each kidney to the urinary
bladder.
The bladder expands and fills with urine until, in a reflex called micturition or
urination, the bladder contracts and expels urine through a single tube, the urethra.
The urethra in males exits the body through the shaft of the penis.
In females, the urethral opening is found anterior to the openings of the vagina and
anus. Bc of the shorter length of the female urethra and its proximity to bacteria
leaving the large intestine, women are more prone than men to develop bacterial
infections of the bladder and kidneys, or urinary tract infections (UTIs).
The most common cause of UTIs is the bacterium Escerichia coli, a normal inhabitant
of the human large intestine. E. coli is not harmful while restricted to the lumen of
large intestine, but its pathogenic (=disease causing), if it gets into the urethra.
Most common symptoms of UTI are pain or burning during urination and increased
frequency of urination.
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