📖 Physiology
Regulation of glomerular filtration
PhysiologyRegulation of glomerular filtration :
1. Extrinsic regulation :
- Neural regulation : sympathetic and parasympathetic nervous system which causes vasoconstriction or vasodilation respectively .
- Humoral regulation : Vasoactive substances may affect the GFR , vasoconstrictive substances like endothelin ,Angiotensin II , Norepinephrine , prostaglandine F2 may constrict the afferent arteriole and thus decrease GFR , while the vasodilative agents like dopamine , NO , ANP , Prostaglandines E2 may dilate the afferent arteriole and thus increase the filtration rate .
2. Intrinsic regulation :
- Myogenic theory ( as in the intrinsic regulation of cardiac output) .
- Tubuloglomerular feedback: occurs by cells of the juxtaglomerular apparatus that is composed of specific cells of the distal tubules when it passes between afferent and efferent arterioles ( macula densa cells ) , these cells sense changes in flow inside the tubules and inform specific cells in the afferent arteriole (granular cells ) , the later secrete vasoactive substances that affect the diameter of the afferent arteriole.
MECHANISM OF HORMONE ACTION
PhysiologyHormones are carried by the blood throughout the entire body, yet they affect only certain cells. The specific cells that respond to a given hormone have receptor sites for that hormone.
This is sort of a lock and key mechanism. If the key fits the lock, then the door will open. If a hormone fits the receptor site, then there will be an effect. If a hormone and a receptor site do not match, then there is no reaction. All of the cells that have receptor sites for a given hormone make up the target tissue for that hormone. In some cases, the target tissue is localized in a single gland or organ. In other cases, the target tissue is diffuse and scattered throughout the body so that many areas are affected.
Hormones bring about their characteristic effects on target cells by modifying cellular activity. Cells in a target tissue have receptor sites for specific hormones. Receptor sites may be located on the surface of the cell membrane or in the interior of the cell.
In general those protein hormones are unable to diffuse through the cell membrane and react with receptor sites on the surface of the cell. The hormone receptor reaction on the cell membrane activates an enzyme within the membrane, called adenyl cyclase, which diffuses into the cytoplasm. Within the cell, adenyl cyclase catalyzes or starts the process of removal of phosphates from ATP to produce cyclic adenosine monophosphate or c AMP. This c AMP activates enzymes within the cytoplasm that alter or change the cellular activity. The protein hormone, which reacts at the cell membrane, is called the first messenger. c Amp that brings about the action attributed to the hormone is called the second messenger. This type of action is relatively rapid because the precursors are already present and they just needed to be activated in some way.
Neurons
PhysiologyNeurons :
Types of neurons based on structure:
a multipolar neuron because it has many poles or processes, the dendrites and the axon. Multipolar neurons are found as motor neurons and interneurons. There are also bipolar neurons with two processes, a dendrite and an axon, and unipolar neurons, which have only one process, classified as an axon.. Unipolar neurons are found as most of the body's sensory neurons. Their dendrites are the exposed branches connected to receptors, the axon carries the action potential in to the central nervous system.
Types of neurons based on function:
- motor neurons - these carry a message to a muscle, gland, or other effector. They are said to be efferent, i.e. they carry the message away from the central nervous system.
- sensory neurons - these carry a message in to the CNS. They are afferent, i.e. going toward the brain or spinal cord.
- interneuron (ie. association neuron, connecting neuron) - these neurons connect one neuron with another. For example in many reflexes interneurons connect the sensory neurons with the motor neurons.
AdenosineTriphosphate (ATP)
PhysiologyAdenosineTriphosphate (ATP)
- Animal cells cannot directly use most forms of energy
- Most cellular processes require energy stored in the bonds of a molecule, adenosine triphosphate (ATP)
- ATP is referred to as the energy currency of the cell
It is a nucleotide, formed from:
- the base adenine (the structure with 2 rings),
- the 5 carbon sugar deoxyribose (one ring)
- 3 phosphates
Energy is stored in the bonds between the phosphates and is released when the bonds are broken