F(x) = Control of the volume and composition of body fluids, Substance excretion and hormone production.
It can do it with those mechanisms:
- REGUTION OF THE ION CONCENTRATION = sodium, potassium, bicarbonate, calcium, inorganic phosphate
- REGULATION OF THE DISPOSAL OF LIQUIDS = control of the elimination or recovery of liquids.
- REGULATION OF THE PH OF THE BLOOD = control of elimination of H+ in urine.
Excretion of substances:
- ENDOGENOUS SUBSTANCES = urea, uric acid, bilirubin, hormones
- EXOGENOUS SUBSTANCES = drugs, pesticides, chemicals
ENDOCRINE FUNCTION
RENIN = a role in secretion of aldosterone, a hormone that helps control water and salt balance in the body.
EPO = stimulates the bone marrow stem cells to increase the production of red boood cells.
VIT D3 = role in bone metabolism and Ca2+ homeostasis.
They produce and secrete: vitamin D → Calcitriol
URINE FORMATION
3 process in coordination that end in the formation of urine:
• FILTRATION, (fluid movement) renal glomerulus → lumen of nephron
• REABSORPTION, (molecule movement) renal tubules → peritubular capillaries
• SECRETION, (molecule movement) peritubular capillaries → tubule → excretion
FILTERED AMOUNT (F) -
REABSORPTION AMOUNT (R) +
SECRETED AMOUNT (S)
=
AMOUNT OF EXCRETED SOLUTE (E)
Substances that:
only filter = creatinin
filtered and then partially reabsorbed = sodium, chloride
filtered and then completely reabsorbed = glucose, amino acids
filtered and secreted = potassium, organic acids, bases
GLOMERULAR FILTRATION
passage of liquids and dissolved substances through the wall of the glomerular
capillaries, which together with other structures make up the filtration barrier. There are
substances that are:
EASILY FILTERED = hydrosoluble, free fraction, low MM
NOT PROPERLY FILTERED = liposoluble, protein-bound fraction, high MM
GLOMERULAR FILTRATION RATE (GFR )= volume of fluid that seeps into Bowman's
capsule per unit time. GFR depends fundamentally on two factors: Filtration coefficient,
and Total filtration pressure (depends on: Blood pressure and Renal blood flow).
Determinate by:
• INTRINSIC CONTROL or SELF-REGULATION, the kidney help maintain constant
blood flow, depend from myogenic response (resistere alle variazioni di pressione
interne per mantere un flusso costante) and tuboglomerular feedback (equilibrio
nella filtrazione glomerulare e nel flusso sanguigno renale).
• NERVOUS CONTROL, sympathetic activation → vasoconstriction → -blood flow →
-GFR
Caused by massive haemorrhages, dehydration, hypovolemia
• HUMORAL CONTROL,
increase = nitric oxide, prostaglandins
decrease = endothelin, adrenaline, noradrenaline
TUBULAR REABSORPTION
The filtrate also contains many useful substances (water,
glucose, amino acids and ions), which must be collected from
the filtrate and returned to the blood. Tubular cells are
“transporters”, which take the necessary substances from the
filtrate and pass them to the extracellular space, from where
they are reabsorbed by the blood. Therefore, the primary
function of the renal tubules is the reabsorption of solutes and
H2O from the lumen of the tubules into plasma by active
transport.
• IN THE PROXIMAL TUBULE, greatest contribution to reabsorption. The proximal tubule
reabsorbs: 70% filtered water, 100% filtered glucose, 100% filtered amino acids, large amount of
ions.
• IN THE LOOP OF HENLE, reabsorb 15% filtered water (→ decreasing loop of Henle), and 25%
filtered NaCl (ascending loop of Henle). The reabsorption of water occurs exclusively in the thin
descending part (the ascending branch is impermeable to water). The reabsorption of NaCl in
the loop of Henle occurs in the ascending part. As the ascending limb does not reabsorb water,
reduces the osmolarity of the tubular fluid. For all this,produces a liquid that is diluted with
respect to plasma, the ascending limb of Henle's loop is also called the
•IN THE DISTAL AND COLLECTING TUBULES, reabsorb 8% of filtered NaCl and 8-17% water
(variable amount). Tubular epithelial cells have hormone receptors that regulate the transport of
water and solutes, so that water reabsorption does not always follow reabsorption of solutes.
If ↑ permeability → CONCENTRATED URINE.
If ↓ permeability → DILUTED URINE.
REGULATION OF ABSORPTION PROCESS
Hormones that increase the reabsorption of H2O and/or Na+ = aldosterone (water and sodium),
ADH (water)
Hormones that decrease the reabsorption of H2O and/or Na+ = ANP
TUBULAR SECRETION
Tubular secretion is the opposite of tubular reabsorption and involves the transfer of materials from the blood into the tubular fluid. It is an active process.
URINE COMPOSITION
95% water with various substances dissolved in it:
- INTROGENATED WASTE, urea, ammonia, uric acid and creatinin.
- ELECTROLITES, sodium, potassium, ammonium, bicarbonate, phosphate.
- TOXINS, bacterial toxins that leave the organism through the urine.
- PIGMENTS, urocromes
- HORMONES
Usually is yellow and clear, the color is due to a pigment that is the result of the
destruction of hemoglobin in the body. More solutes = intense yellow color. But if it is
retained in a container, it will acquire an ammonia odor caused by the action of bacteria
on the urine solutes. Slightly acid (around 6).
ABNORMAL COMPONENTS: albumin, glucose, erythrocytes, bilirubin,microorganisms.
URINATION
Once the filtrate leaves the collecting ducts, its composition cannot be modified. The
urine falls into the renal pelvis, continue in the ureters.
The distension that occurs in the renal pelvis due to the fall of urine triggers a series of
peristaltic movements in the ureters (with a frequency of 5-10 / minute), that cause an
advance of urine into the bladder.
URINATION or DIURESIS = emptying the urinary bladder.
innervation of the urinary tract:
SYMPATHETIC, favors the filling of the bladder
PARASYMPATHETIC, favors contractions that push the urine towards the urethra
SOMATIC, inhibits contraction of external sphincter and facilitates urination
REGULATION OF TUBULAR REABSORPTION AND SECRETION
H. that regulate H2O levels = ADH
H. that regulate H2O and NaCl levels = R-A-A, ANP
Non-h. mechanisms involved in the regulation of liquids and NaCl = thirst, salt appetite, sympathetic NS
- ADH (antidiuretic h.), response to a water deficit, it increases the permeability to water in the main cells of the distal tubules and collectors.
Water deficit → ↑ ADH → concentrated urin Water excess → ↓ ADH → diluted urine
- RENIN - ANGIOTENSIN - ALDOSTERONE SYSTEM, the RAAS helps regulate blood pressure and fluid balance. When blood pressure is low, the system is triggered to
increase it through vasoconstriction, reabsorption of sodium and water, and stimulation of aldosterone production.
- NATRIURETIC PEPTIDE (ANP and BNP), secreted by cardiac muscle cells in the heart ventricles. Inhibits the reabsorption of sodium and water in the PCT and collecting
tubule. Inhibits the secretion of ADH and aldosterone.
- NERVOUS REGULATION, When the volume of extracellular fluid decreases, the activation of baroreceptors causes stimulation of the sympathetic NS.
THIRST, The thirst center (in the hypothalamus) regulates the urge to drink. Dehydration stimulates the thirst center by: ↑angiotensin II, hypothalamic
osmoreceptors, Decreased saliva (neurons in the mouth that detect dryness), Baroreceptors that detect ↓AP
factors that favor dilution of urine = ↓ ADH, ↓ RAA, ↓ sympathetic NS, ↑ ANP
factors that favor concentration of urine = ↑ ADH, ↑ RAA, ↑ sympathetic NS, ↓ ANP
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