NEET MDS Lessons
Physiology
Cells, cytoplasm, and organelles:
- Cytoplasm consists of a gelatinous solution and contains microtubules (which serve as a cell's cytoskeleton) and organelles
- Cells also contain a nucleus within which is found DNA (deoxyribonucleic acid) in the form of chromosomes plus nucleoli (within which ribosomes are formed)
- Organelles include:
- Endoplasmic reticulum : 2 forms: smooth and rough; the surface of rough ER is coated with ribosomes; the surface of smooth ER is not , Functions include: mechanical support, synthesis (especially proteins by rough ER), and transport
- Golgi complex consists of a series of flattened sacs (or cisternae) functions include: synthesis (of substances likes phospholipids), packaging of materials for transport (in vesicles), and production of lysosomes
- Lysosome : membrane-enclosed spheres that contain powerful digestive enzymes , functions include destruction of damaged cells & digestion of phagocytosed materials
- Mitochondria : have double-membrane: outer membrane & highly convoluted inner membrane
- inner membrane has folds or shelf-like structures called cristae that contain elementary particles; these particles contain enzymes important in ATP production
- primary function is production of adenosine triphosphate (ATP)
- Ribosome-:composed of rRNA (ribosomal RNA) & protein , primary function is to produce proteins
- Centrioles :paired cylindrical structures located near the nucleas , play an important role in cell division
- Flagella & cilia - hair-like projections from some human cells
- cilia are relatively short & numerous (e.g., those lining trachea)
- a flagellum is relatively long and there's typically just one (e.g., sperm)
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- Villi Projections of cell membrane that serve to increase surface area of a cell (which is important, for example, for cells that line the intestine)
Levels of Organization:
CHEMICAL LEVEL - includes all chemical substances necessary for life (see, for example, a small portion - a heme group - of a hemoglobin molecule); together form the next higher level
CELLULAR LEVEL - cells are the basic structural and functional units of the human body & there are many different types of cells (e.g., muscle, nerve, blood)
TISSUE LEVEL - a tissue is a group of cells that perform a specific function and the basic types of tissues in the human body include epithelial, muscle, nervous, and connective tissues
ORGAN LEVEL - an organ consists of 2 or more tissues that perform a particular function (e.g., heart, liver, stomach)
SYSTEM LEVEL - an association of organs that have a common function; the major systems in the human body include digestive, nervous, endocrine, circulatory, respiratory, urinary, and reproductive.
There are two types of cells that make up all living things on earth: prokaryotic and eukaryotic. Prokaryotic cells, like bacteria, have no 'nucleus', while eukaryotic cells, like those of the human body, do.
Gonadotropin-releasing hormone (GnRH)
GnRH is a peptide of 10 amino acids. Its secretion at the onset of puberty triggers sexual development.
Primary Effects
FSH and LH Relaese
Secondary Effects
Increases estrogen and progesterone (in females)
testosterone Relaese (in males)
Growth hormone-releasing hormone (GHRH)
GHRH is a mixture of two peptides, one containing 40 amino acids, the other 44. GHRH stimulates cells in the anterior lobe of the pituitary to secrete growth hormone (GH).
Corticotropin-releasing hormone (CRH)
CRH is a peptide of 41 amino acids. Its acts on cells in the anterior lobe of the pituitary to release adrenocorticotropic hormone (ACTH) CRH is also synthesized by the placenta and seems to determine the duration of pregnancy. It may also play a role in keeping the T cells of the mother from mounting an immune attack against the fetus
Somatostatin
Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28. Somatostatin acts on the anterior lobe of the pituitary to
- inhibit the release of growth hormone (GH)
- inhibit the release of thyroid-stimulating hormone (TSH)
Somatostatin is also secreted by cells in the pancreas and in the intestine where it inhibits the secretion of a variety of other hormones.
Antidiuretic hormone (ADH) and Oxytocin
These peptides are released from the posterior lobe of the pituitary
Proteins:
- about 50 - 60% of the dry mass of a typical cell
- subunit is the amino acid & amino acids are linked by peptide bonds
- 2 functional categories = structural (proteins part of the structure of a cell like those in the cell membrane) & enzymes
Enzymes are catalysts. Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction
Regulation 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.
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Damage to Spinal Nerves and Spinal Cord |
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Damage |
Possible cause of damage |
Symptoms associated with innervated area |
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Peripheral nerve |
Mechanical injury |
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy. Loss of sensation |
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Posterior root |
Tabes dorsalis |
Paresthesia. Intermittent sharp pains. Decreased sensitivity to pain. Loss of reflexes. Loss of sensation. Positive Romberg sign. High stepping and slapping of feet. |
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Anterior Horn |
Poliomyelitis |
Loss of muscle tone. Loss of reflexes. Flaccid paralysis. Denervation atrophy |
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Lamina X (gray matter) |
Syringomyelia |
Bilateral loss of pain and temperature sense only at afflicted cord level. Sensory dissociation. No sensory impairment below afflicted level |
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Anterior horn and lateral corticospinal tract |
Amyotrophic lateral sclerosis |
Muscle weakness. Muscle atrophy. Fasciculations of hand and arm muscles. Spastic paralysis |
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Posterior and lateral funiculi |
Subacute combined degeneration |
Loss of position sense. Loss of vibratory sense. Positive Romberg sign. Muscle weakness. Spasticity. Hyperactive tendon reflexes. Positive Babinski sign. |
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Hemisection of the spinal cord |
Mechanical injury |
Brown-Sequard syndrome |
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Below cord level on injured side |
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Flaccid paralysis. Hyperactive tendon reflexes. Loss of position sense. Loss of vibratory sense. Tactile impairment |
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Below cord level on opposite side beginning one or two segments below injury |
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Loss of pain and temperature |
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Characteristics of Facilitated Diffusion & Active Transport - both require the use of carriers that are specific to particular substances (that is, each type of carrier can 'carry' one type of substance) and both can exhibit saturation (movement across a membrane is limited by number of carriers & the speed with which they move materials