FISIOLOGI SISTEM EKSKRESI

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Fisiologi hewan 2

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Proses Pengeluaran

Berdasarkan zat yang dibuang, proses pengeluaran pada manusia dibedakan menjadi: Defekasi: pengeluaran zat sisa hasil

pencernaan (feses) Ekskresi: pengeluaran zat sisa hasil

metabolisme (CO2, keringat dan urine) Sekresi: pengeluaran getah yang masih

berguna bagi tubuh (enzim dan hormon)

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Sistem Ekskresi

Adalah sistem pengeluaran zat-zat sisa metabolisme yang tidak berguna bagi tubuh dari dalam tubuh, seperti:

Menghembuskan gas CO2 ketika kita bernafas pulmo

Berkeringat Buang air kecil (urine)

1. Ginjal 2. Kulit 3. Hati 4. Paru-paru

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Alat Ekskresi manusia

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ALAT-ALAT EKSKRESI

∗ A. Struktur Ginjal

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GINJAL

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Functions of the Urinary System The urinary system produces urine and conducts it to outside the body. As the kidneys produce urine, they carry out four functions: 1. excretion of metabolic wastes, 2. maintenance of water-salt balance, 3. maintenance of acid-base balance, 4. and secretion of hormones.

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Excretion of Metabolic Wastes The kidneys excrete metabolic wastes, notably nitrogenous wastes. Urea is the primary nitrogenous end product of metabolism in human beings, but humans also excrete some ammonium, creatinine, and uric acid. Urea is a by-product of amino acid metabolism. The breakdown of amino acids in the liver releases ammonia, which the liver combines with carbon dioxide to produce urea. Ammonia is very toxic to cells, but urea is much less toxic. Because it is less toxic, less water is required to excrete urea. Creatine phosphate is a high-energy phosphate reserve molecule in muscles. The metabolic breakdown of creatine phosphate results in creatinine. The breakdown of nucleotides, such as those containing adenine and thymine, produces uric acid. Uric acid is rather insoluble. If too much uric acid is present in blood, crystals form and precipitate out. Crystals of uric acid sometimes collect in the joints, producing a painful ailment called gout.

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Maintenance of Water-Salt Balance A principal function of the kidneys maintain the appropriate water-salt balance of the blood. As we shall see, blood volume is intimately associated with the salt balance of the body. Salts, such as NaCl, have the ability to cause osmosis, the diffusion of water—in this case, into the blood. The more salts there are in the blood, the greater the blood volume and the greater the blood pressure. In this way, the kidneys are involved in regulating blood pressure. The kidneys also maintain the appropriate level of other ions (electrolytes), such as potassium ions (K), bicarbonate ions (HCO3), and calcium ions (Ca2), in the blood.

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Maintenance of Acid-Base Balance The kidneys regulate the acid-base balance of the blood. In order for a person to remain healthy, the blood pH should be just about 7.4. The kidneys monitor and control blood pH, mainly by excreting hydrogen ions (H) and reabsorbing the bicarbonate ions (HCO3) as needed to keep blood pH at about 7.4. Urine usually has a pH of 6 or lower because our diet often contains acidic foods.

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Secretion of Hormones The kidneys assist the endocrine system in hormone secretion. The kidneys release renin, a substance that leads to the secretion of the hormone aldosterone from the adrenal cortex, the outer portion of the adrenal glands, which lie atop the kidneys. Aldosterone promotes the reabsorption of sodium ions (Na) by the kidneys. Whenever the oxygen-carrying capacity of the blood is reduced, the kidneys secrete the hormone erythropoietin, which stimulates red blood cell production. The kidneys also help activate vitamin D from the skin. Vitamin D is the precursor of the hormone calcitriol, which promotes calcium (Ca2) absorption from the digestive tract.

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Aldosterone Hormones control the reabsorption of sodium at the distal convoluted tubule. Aldosterone, a hormone secreted by the adrenal cortex, promotes the excretion of potassium ions (K) and the reabsorption of sodium ions (Na). The release of aldosterone is set in motion by the kidneys themselves. The juxtaglomerular apparatus is a region of contact between the afferent arteriole and the distal convoluted tubule. When blood volume, and therefore blood pressure, is not sufficient to promote glomerular filtration, the juxtaglomerular apparatus secretes renin.

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Renin is an enzyme that changes angiotensinogen (a large plasma protein produced by the liver) into angiotensin I. Later, angiotensin I is converted to angiotensin II, a powerful vasoconstrictor that also stimulates the adrenal cortex to release aldosterone. The reabsorption of sodium ions is followed by the reabsorption of water. Therefore, blood volume and blood pressure increase.

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Juxtaglomerular apparatus. This drawing shows that the afferent arteriole and the distal convoluted tubule usually lie next to each other. The juxtaglomerular apparatus occurs where they touch. The juxtaglomerular apparatus secretes renin, a substance that leads to the release of aldosterone by the adrenal cortex. Reabsorption of sodium ions followed by water then occurs. Therefore, blood volume and blood pressure increase.

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STRUKTUR GINJAL

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Anatomy of kidney

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Glomerular filtration whole blood enters the afferent arteriole and the glomerulus. Due to glomerular blood pressure, water and small molecules move from the glomerulus to the inside of the glomerular capsule. This is a filtration large molecules and formed elements are unable to pass through the capillary wall. Blood in the glomerulus the filterable components and the nonfilterable components:

1. Glomerular Filtration

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Filterable Nonfilterable Blood Components Blood Components Water Formed elements (blood Nitrogenous wastes cells and platelets) Nutrients Plasma proteins Salts (ions)

Nephrons in the kidneys filter 180 liters of water per day, along with a considerable amount of small molecules (such as glucose) and ions (such as sodium). If the composition of urine were the same as that of the glomerular filtrate, the body would continually lose water, salts, and nutrients. Therefore composition of the filtrate must be altered as this fluid passes through the remainder of the tubule.

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Tubular reabsorption molecules and ions are both passively and actively reabsorbed from the nephron into the blood of the peritubular capillary network. Na (sodium) actively reabsorbed, Cl (Chloride) follow passively. The reabsorption of salt (NaCl) increases the osmolarity of the blood compared to the filtrate, and therefore water moves passively from the tubule into the blood. About 67% of Na is reabsorbed at the proximal convoluted tubule. Nutrients such as glucose and amino acids also return to the blood at the proximal convoluted tubule. This is a selective process because only molecules recognized by carrier molecules are actively reabsorbed.

2. Tubular Reabsorption

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Glucose is an example of a molecule that ordinarily is completely reabsorbed because there is a plentiful supply of carrier molecules for it. However, every substance has a maximum rate of transport, and after all its carriers are in use, any excess in the filtrate will appear in the urine. For example, as reabsorbed levels of glucose approach 1.8–2 mg/ml plasma, the rest appears in the urine. In diabetes mellitus, excess glucose occurs in the blood, and then in the filtrate, and then in the urine, because the liver and muscles have failed to store glucose as glycogen, and the kidneys cannot reabsorb all of it. The presence of glucose in the filtrate increases its osmolarity compared to that of the blood, and therefore less water is reabsorbed into the peritubular capillary network. The frequent urination and increased thirst experienced by untreated diabetics are due to the fact that water is not being reabsorbed.

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Filtrate that enters the proximal convoluted tubule two portions: components that are reabsorbed from the tubule into the blood, and components that are not reabsorbed and continue to pass through the nephron further processed into urine: Reabsorbed Filtrate Nonreabsorbed Filtrate Components Components Most water Some water Nutrients Much nitrogenous waste Required salts (ions) Excess salts (ions) The substances that are not reabsorbed become the tubular fluid, which enters the loop of the nephron.

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Tubular secretion a second way by which substances are removed from blood and added to the tubular fluid. Hydrogen ions, potassium ions, creatinine, and drugs such as penicillin are some of the substances that are moved by active transport from the blood into the distal convoluted tubule. In the end urine contains (1) substances that have undergone glomerular filtration but have not been reabsorbed, and (2) substances that have undergone tubular secretion.

3. Tubular Secretion

HORMON ANTI DIURETIK (ADH) YANG DIHASILKAN OLEH KELENJAR HIPOFISIS POSTERIOR AKAN MEMPENGARUHI PENYERAPAN AIR PADA BAGIAN TUBULUS DISTAL KARENA MENINGKATKAN PERMEABILITIAS SEL TERHADAP AIR.

∗ JIKA HORMON ADH RENDAH MAKA PENYERAPAN AIR BERKURANG SEHINGGA URIN MENJADI BANYAK DAN ENCER.

∗ SEBALIKNYA, JIKA HORMON ADH BANYAK, PENYERAPAN AIR BANYAK SEHINGGA URIN SEDIKIT DAN PEKAT.

∗ KEHILANGAN KEMAMPUAN MENSEKRESI ADH MENYEBABKAN PENYAKTI DIABETES INSIPIDUS. PENDERITANYA AKAN MENGHASILKAN URIN YANG SANGAT ENCER.

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ADH MEMPENGARUHI PRODUKSI URIN

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Antidiuretic Hormone (ADH) ADH released by the posterior lobe of the pituitary plays a role in water reabsorption at the collecting duct. In order to understand the action of this hormone, consider its name. Diuresis means flow of urine, and antidiuresis means against a flow of urine. When ADH is present, more water is reabsorbed (blood volume and pressure rise), and a decreased amount of urine results. In practical terms, if an individual does not drink much water on a certain day, the posterior lobe of the pituitary releases ADH, causing more water to be reabsorbed and less urine to form. On the other hand, if an individual drinks a large amount of water and does not perspire much, ADH is not released. In that case, more water is excreted, and more urine forms.

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THAT’S ALL FOR NOW…. THANKS !!