Renal system: L35 - Functions of the Kidney & Nephron function Flashcards
Explain the kidney function of excretion.
The kidneys excrete any excess intake of water or electrolytes, which is vital for maintaining homeostasis and keeping the volume and composition of the extracellular fluid within acceptable limits.
The waste products of metabolism are also excreted by the kidneys including nitrogenous wastes like urea and uric acid, hormones and bile pigments.
Explain the kidney function of hormone production.
The kidneys produce a number of hormones including: calcitriol, EPO, renin, dopamine, prostaglandins and kallikrein.
Calcitriol is the active form of vitamin D, an enzyme found in the kidneys allows this conversion from vitamin D to calcitriol. Calcitriol is important for calcium balance and bone mineralisation. Chronic renal failure = bone problems.
EPO is a hormone that stimulates production of RBCs in the bone marrow. Kidneys produce EPO in response to low levels of oxygen. Chronic renal failure = anaemia.
Explain the kidney function of metabolism.
Ammonia NH3 is synthesised and excreted by the kidneys, processes that are important in both maintaining nitrogen (N) balance and acid-base balance.
Although most gluconeogenesis occurs in the liver, some also takes place in the cortex of the kidneys.
Gluconeogenesis is an important metabolic pathway that allows us to make glucose from amino acid precursors.
Explain the kidney function of homeostasis.
Acid-base balance = excrete acids that cannot be turned into gases. Can also secrete bicarbonate to buffer bodily acids.
Fluid balance = Urine output adjusted to maintain volume and osmolarity.
Electrolyte balance = Most electrolytes are kept in balance by what kidneys excrete rather than what the intestines absorb.
Discuss the kidneys’ role in electrolyte K+ homeostasis.
Potassium concentration is vital for many processes that require electrical excitability of cells. It is obtained from what we absorb in our diet. The only regulated excretion of potassium occurs via the kidneys. If there is high K+ intake excretion by the kidneys increases gradually to match our high intake until the plasma K+ concentration stabilises at a value that is only slightly higher than normal. If there is low K+ intake excretion by the kidneys decrease gradually until plasma K+ concentration stabilises at a value that is only slightly lower than normal.
Explain the three basic functions of the nephron.
Filtration: creates a plasma-like filtrate of the blood with no RBCs or WBCs and virtually no protein.
Reabsorption: removes useful solutes from filtrate and returns them to blood. We filtrate 180L but only urinate 1.5L per day, so a lot of reabsorption takes place.
Secretion: Additional waste can be thrown out from the blood in the peritubular capillaries and vasa recta into the filtrate of the nephron.
Explain how the handling of different substances occurs in the kidneys.
Once they have been filtered, different substances are handled differently. For example, almost all water is absorbed but it depends on how hydrated you are, glucose is all reabsorbed, potassium is secreted by the tubules, creatine is neither secreted nor reabsorbed. Various substances get handled differently in different parts of the nephron. For example glucose is only reabsorbed in the PT, water is reabsorbed in most parts except the DT, potassium is reabsorbed and secreted by different parts of the tubule.
Describe the different processes that occur in different parts of nephron.
Glomerulus - filtration
PT - bulk reabsorption
DT - Fine-tuning of electrolytes
CD - Fine-tuning of water reabsorption.
