Which force favors filtration

When blood pressure drops, the same capillaries relax to maintain blood flow and filtration rate. The net result is a relatively steady flow of blood into the glomerulus and a relatively steady filtration rate in spite of significant systemic blood pressure changes.

One third of this is 10, and when you add this to the diastolic pressure of 80, you arrive at a calculated mean arterial pressure of 90 mm Hg. Therefore, if you use mean arterial pressure for the GBHP in the formula for calculating NFP, you can determine that as long as mean arterial pressure is above approximately 60 mm Hg, the pressure will be adequate to maintain glomerular filtration.

Blood pressures below this level will impair renal function and cause systemic disorders that are severe enough to threaten survival. This condition is called shock. It is vital that the flow of blood through the kidney be at a suitable rate to allow for filtration and yet not too fast to overwhelm the reabsorbing potential of the nephron tubule. This rate determines how much solute is retained or discarded, how much water is retained or discarded, and ultimately, the osmolarity of blood and the blood pressure of the body.

Glomerular filtration has to be carefully and thoroughly controlled because the simple act of filtrate production can have huge impacts on body fluid homeostasis and systemic blood pressure.

Due to these two very distinct physiological needs, the body employs two very different mechanisms to regulate GFR. The kidney can control itself locally through intrinsic controls, also called renal autoregulation.

These intrinsic control mechanisms maintain filtrate production so that the body can maintain fluid, electrolyte, and acid-base balance and also remove wastes and toxins from the body.

There are also control mechanisms that originate outside of the kidney, the nervous and endocrine systems, and are called extrinsic controls.

The nervous system and hormones released by the endocrine systems function to control systemic blood pressure by increasing or decreasing GFR to change systemic blood pressure by changing the fluid lost from the body. The kidneys are very effective at regulating the rate of blood flow over a wide range of blood pressures. Your blood pressure will decrease when you are relaxed or sleeping. It will increase when exercising.

Yet, despite these changes, the filtration rate through the kidney will change very little. This is due to two internal autoregulatory mechanisms that operate without outside influence: the myogenic mechanism and the tubuloglomerular feedback mechanism. The myogenic mechanism regulating blood flow within the kidney depends upon a characteristic shared by most smooth muscle cells of the body. When you stretch a smooth muscle cell, it contracts; when you stop, it relaxes, restoring its resting length.

This mechanism works in the afferent arteriole that supplies the glomerulus and can regulate the blood flow into the glomerulus. When blood pressure increases, smooth muscle cells in the wall of the arteriole are stretched and respond by contracting to resist the pressure, resulting in little change in flow. This vasoconstriction of the afferent arteriole acts to reduce excess filtrate formation, maintaining normal NFP and GFR. Reducing the glomerular pressure also functions to protect the fragile capillaries of the glomerulus.

When blood pressure drops, the same smooth muscle cells relax to lower resistance, increasing blood flow. The vasodilation of the afferent arteriole acts to increase the declining filtrate formation, bringing NFP and GFR back up to normal levels.

The tubuloglomerular feedback mechanism involves the juxtaglomerular JG cells, or granular cells, from the juxtaglomerular apparatus JGA and a paracrine signaling mechanism utilizing ATP and adenosine.

These juxtaglomerular cells are modified, smooth muscle cells lining the afferent arteriole that can contract or relax in response to the paracrine secretions released by the macula densa. This mechanism stimulates either contraction or relaxation of afferent arteriolar smooth muscle cells, which regulates blood flow to the glomerulus Table Recall that the DCT is in intimate contact with the afferent and efferent arterioles of the glomerulus. The increased fluid movement more strongly deflects single nonmotile cilia on macula densa cells.

This increased osmolarity of the filtrate, and the greater flow rate within the DCT, activates macula densa cells to respond by releasing ATP and adenosine a metabolite of ATP. ATP and adenosine act locally as paracrine factors to stimulate the myogenic juxtaglomerular cells of the afferent arteriole to constrict, slowing blood flow into the glomerulus. This vasoconstriction causes less plasma to be filtered, which decreases the glomerular filtration rate GFR , which gives the tubule more time for NaCl reabsorption.

Conversely, when GFR decreases, less NaCl is in the filtrate, and most will be reabsorbed before reaching the macula densa, which will result in decreased ATP and adenosine, allowing the afferent arteriole to dilate and increase GFR.

Definition Thin-walled, larger than capillaries but smaller than arterioles. Formed from network of capillaries and carry blood to veins. Term Veins. Definition Thin-walled, fairly muscular, highly distensible. Carry blood from venules back to heart. Term Active Hyperemia. Definition Increased blood flow to due an increase in metabolic activity. Term Reactive Hyperemia. Definition Increased blood flow in response to a previous reduction in blood flow.

Term Vasoconstriction. Definition Increased resistance to blood flow. Term Vasodilation. Definition Decreased resistance to blood flow. Term Myogenic Response. Definition A change in vascular resistance that does not require the action of sympathetic nerves, bloodborne hormones, or other chemical agents.

Term What happens when norpeinephrine binds to alpha adrenergic receptors? Term What happens when epinephrine binds to beta 2 adrenergic receptors? Definition Activation of the cAMP second messenger system resulting in vasodilation. Term Epinephrine has the greatest affinity for which type of receptors? Definition Beta 2 receptors. Term What two hormones regulate arteriolar resistance, cause vasoconstriction and an increase in MAP?

Term Vasopressin. Definition A hormone secreted by the posterior pituitary gland that limits urine output and causes vasoconstriction. Term Angiotensin II. Definition A protein derived from angiotensin in a two step process. Angiotensin is coverted to angiotensin I by renin. Angiotensin I is converted to angiotensin II by angiotensin converting enzyme.

Term What happens when epinephrine binds to alpha adrenergic receptors? Definition Vasoconstriction. Term Continous Capillaries. Definition Endothelial cells are joined together with tight junctions, limiting the passage of some molecules. Term Fenestrated Capillaries.

Definition Endothelial cells possess relatively large pores that allow rapid diffusion of small water-soluble substances. Term Edema. Thus, fluid generally moves out of the capillary and into the interstitial fluid.

This process is called filtration. What is the difference between oncotic and hydrostatic pressure? Osmotic pressure is a measure of the concentration of solutions.

It does not cause actual, physical pressure. High osmotic pressure in the blood will cause water to be taken out of the cells. The kidneys usually maintain osmotic pressure under very tight control, so elevated osmotic pressure usually is abnormal. A resistance artery is small diameter blood vessel in the microcirculation that contributes significantly to the creation of the resistance to flow and regulation of blood flow. Resistance arteries are usually arterioles or end-points of arteries.

Hydrostatic pressure is the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above.

As one of the key components of an aquarium, filtration is responsible for moving and cleaning the tank water, making it safe for fish to live in.

The three main types of filtration are mechanical, biological, and chemical filtration. Filtration is a process used to separate solids from liquids or gases using a filter medium that allows the fluid to pass through but not the solid.

The term " filtration " applies whether the filter is mechanical, biological, or physical. The fluid that passes through the filter is called the filtrate. Examples of filtration include. The coffee filter to keep the coffee separate from the grounds.

HEPA filters in air conditioning to remove particles from air. Belt filters to extract precious metals in mining. Horizontal plate filter, also known as Sparkler filter. Simple Filtration is a physical method to screen out the insoluble solid from solution by a physical barrier, filter paper. The picture at the left shows a set-up for simple filtration. It contains a filter funnel, a folded filter paper and a beaker for collecting the filtrate. Filtration : Filtration is a process by which insoluble solids can be removed from a liquid by using a filter paper.