NEET MDS Synopsis
Micturition and Micturition reflex
Physiology
Micturition (urination) is a process, by which the final urine is eliminated out of the body .
After being drained into the ureters, urine is stored in urinary bladder until being eliminated.
Bladder is a hollow muscular organ, which has three layers:
- epithelium : Composed of superficial layer of flat cells and deep layer of cuboidal cells.
- muscular layer : contain smooth muscle fibers, that are arranged in longitudinal, spiral and circular pattern . Detrusor muscle is the main muscle of bladder. The thickening of detrusor muscle forms internal urinary sphinctor which is not an actual urinary sphincter. The actual one is the external urinary sphincter, which is composed of striated muscle and is a part of urogenital diaphragm.
- adventitia: composed of connective tissue fibers.
So: There are two phases of bladder function that depend on characterestics of its muscular wall and innervation :
1. Bladder filling : Urine is poured into bladder through the orifices of ureters. Bladder has five peristaltic contraction per minute . These contraction facilitate moving of urine from the ureter to the bladder as prevent reflux of urine into the ureter.. The capacity of bladder is about 400 ml. But when the bladder start filling its wall extends and thus the pressure is not increased with the increased urine volume.
2. Bladder emptying : When bladder is full stretch receptors in bladder wall are excited , and send signals via the sensory branches of pelvic nerves to the sacral plexus. The first urge to void is felt at a bladder volume of about 150 ml. In sacral portion of spinal cord the sensory signals are integrated and then a motor signal is sent to the urinarry blader muscles through the efferent branches of pelvic nerve itself.
In adult people the neurons in sacral portion could be influenced by nerve signals coming from brain ( Micturition center in pons ) that are also influenced by signals coming from cerebral cortex.
So: The sensory signals ,transmitted to the sacral region will also stimulate ascending pathway and the signals be also transmitted to the micturition center in the brain stem and then to the cerebrum to cause conscious desire for urination.
If micturition is not convenient the brain sends signals to inhibit the parasympathetic motor neuron to the bladder via the sacral neurons.
It also send inhibitory signal via the somatomotor pudendal nerve to keep external urinary sphincter contracting.
When micturition is convenient a brain signal via the sacral neurons stimulate the parasympathetic pelvic nerve to cause contraction of detruser muscle via M-cholinergic receptors and causes relaxation of external urinary sphincter and the micturition occurs.
Sympathetic hypogastric nerve does not contribute that much to the micturition reflex. It plays role in prvrntion reflux of semen into urinary bladder during ejaculation by contracting bladder muscles.
Growth hormone
Biochemistry
Growth hormone
Growth hormone (GH or HGH), also known as somatotropin or somatropin, is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans.
Growth hormone is a single-chain polypeptide that is synthesized, stored, and secreted by somatotropic cells within the lateral wings of the anterior pituitary gland.
Regulation of growth hormone secretion
Secretion of growth hormone (GH) in the pituitary is regulated by the neurosecretory nuclei of the hypothalamus. These cells release the peptides Growth hormone-releasing hormone (GHRH or somatocrinin) and Growth hormone-inhibiting hormone (GHIH or somatostatin) into the hypophyseal portal venous blood surrounding the pituitary.
GH release in the pituitary is primarily determined by the balance of these two peptides, which in turn is affected by many physiological stimulators (e.g., exercise, nutrition, sleep) and inhibitors (e.g., free fatty acids) of GH secretion.
Regulation
Stimulators of growth hormone (GH) secretion include peptide hormones, ghrelin, sex hormones, hypoglycemia, deep sleep, niacin, fasting, and vigorous exercise.
Inhibitors of GH secretion include somatostatin, circulating concentrations of GH and IGF-1 (negative feedback on the pituitary and hypothalamus), hyperglycemia, glucocorticoids, and dihydrotestosterone.
Clinical significance
The most common disease of GH excess is a pituitary tumor composed of somatotroph cells of the anterior pituitary. These somatotroph adenomas are benign and grow slowly, gradually producing more and more GH excess. The adenoma may become large enough to cause headaches, impair vision by pressure on the optic nerves, or cause deficiency of other pituitary hormones by displacement.
Metastatic Tumors
General Pathology
Metastatic Tumors
These are the most common malignant tumor of bone. Certain tumors exhibit a distinct skeletal prediliction. In adults more than 75% of skeletal metastases originate from cancers of the prostate, breast, kidney, and lung. In children, neuroblastoma, Wilms' tumor, osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma are the common sources of bony metastases. Most metastases involve the axial skeleton (vertebral column, pelvis, ribs, skull, sternum), proximal femur, and humerus. The radiologic appearance of metastases can be purely osteolytic, purely osteoblastic, or mixed osteolytic-osteoblastic (majority of cases). In lytic lesions (e.g., kidney& lung), the metastatic cells secrete substances such as prostaglandins, interleukins, etc. that stimulate osteoclastic bone resorption; the tumor cells themselves do not directly resorb bone. Similarly, metastases that elicit a blastic response (e.g., prostate adenocarcinoma) do so by stimulating osteoblastic bone formation.
Anterior bite plate
OrthodonticsAnterior bite plate is an orthodontic appliance used
primarily to manage various dental issues, particularly those related to
occlusion and alignment of the anterior teeth. It is a removable appliance that
is placed in the mouth to help correct bite discrepancies, improve dental
function, and protect the teeth from wear.
Indications for Use
Anterior Crossbite:
An anterior bite plate can help correct an anterior crossbite by
repositioning the maxillary incisors in relation to the mandibular
incisors.
Open Bite:
It can be used to help close an anterior open bite by providing a
surface for the anterior teeth to occlude against, encouraging proper
alignment.
Bruxism:
The appliance can protect the anterior teeth from wear caused by
grinding or clenching, acting as a barrier between the upper and lower
teeth.
Space Maintenance:
In cases where anterior teeth have been lost or extracted, an
anterior bite plate can help maintain space for future dental work or
the eruption of permanent teeth.
Facilitation of Orthodontic Treatment:
It can be used as part of a comprehensive orthodontic treatment plan
to help achieve desired tooth movements and improve overall occlusion.
Design and Features
Material: Anterior bite plates are typically made from
acrylic or thermoplastic materials, which are durable and can be easily
adjusted.
Shape: The appliance is designed to cover the anterior
teeth, providing a flat occlusal surface for the upper and lower teeth to
meet.
Retention: The bite plate is custom-fitted to the
patient’s dental arch to ensure comfort and stability during use.
Mechanism of Action
Repositioning Teeth: The anterior bite plate can help
reposition the anterior teeth by providing a surface that encourages proper
occlusion and alignment.
Distributing Forces: It helps distribute occlusal
forces evenly across the anterior teeth, reducing the risk of localized wear
or damage.
Encouraging Proper Function: By providing a stable
occlusal surface, the bite plate encourages proper chewing and speaking
functions.
Management and Care
Patient Compliance: For the anterior bite plate to be
effective, patients must wear it as prescribed by their orthodontist. This
may involve wearing it during the day, at night, or both, depending on the
specific treatment goals.
Hygiene: Patients should maintain good oral hygiene and
clean the bite plate regularly to prevent plaque buildup and maintain oral
health.
Regular Check-Ups: Follow-up appointments with the
orthodontist are essential to monitor progress and make any necessary
adjustments to the appliance.
NORMAL MICROBIAL FLORA
General Microbiology
NORMAL MICROBIAL FLORA
A. Properties. Normal microbial flora describes the population of microorganisms that usually reside in the body. The microbiological flora can be defined as either
1) Resident flora - A relatively fixed population that will repopulate if disturbed,
2) Transient flora - that are derived from the local environment. These microbes usually reside in the body without invasion and can
even prevent infection by more pathogenic organisms, a phenomenon known as bacterial interference.
The flora have commensal functions such as vitamin K synthesis. However, they may cause invasive disease in immunocompromised hosts or if displaced from their normal area.
B. Location. Microbial flora differ in composition depending on their anatomical locations and microenvironments. The distribution of normal microbial flora.
The Temporomandibular Joint
AnatomyThe Temporomandibular Joint
This articulation is a modified hinge type of synovial joint.
The articular surfaces are: (1) the head or condyle of the mandible inferiorly and (2) the articular tubercle and the mandibular fossa of the squamous part of the temporal bone.
An oval fibrocartilaginous articular disc divides the joint cavity into superior and inferior compartments. The disc is fused to the articular capsule surrounding the joint.
The articular disc is more firmly bound to the mandible than to the temporal bone.
Thus, when the head of the mandible slides anterior on the articular tubercle as the mouth is opened, the articular disc slides anteriorly against the posterior surface of the articular tubercle
POLYCYTHEMIA
General Pathology
POLYCYTHEMIA
It is an increase in number of RC per unit volume of blood (Hb more than 1.9.5 gms% and 18 gms% for women)
Causes :
True polycythemia.
- Idiopathic Polythemia vera.
- Secondary to :
o Hypoxia of high altitude , heart disease, chronic lung disease etc.
o Erythopoietin oversecretion as in renal diseases , tumours of liver, kidney and adrenal etc.
o Compensatory in haemogIobinopathies
- Relative polycythemia due to reduction in plasma volume as in dehydration or in redistribution off fluids
Polycythemia vera: It is a myeloprolifeative disorder, usually terminating in myelosclerosis.
Features: are due to hypervolaemic circulation and tendency to tbrombosis and haemorrhage
-Headaches, dizziness and cardiovascular accidents.
-Hypertension.
-Peripheral vascular thrombosis.
-GIT bleeding. retinal haemorrhage.
-Gout.
-Pruritus.
Blood Finding
-Increased Hb. PCV and RBC count.
-Leucocytosis with high alkaline phosphatase.
-Platelets increased.
Marrow picture Hypercellular with increase in precursors of all series
Course Chronic course ending in myelosclerosis or acute leukaemia.
The Parathyroid Glands
Physiology
The Parathyroid Glands
The parathyroid glands are 4 tiny structures embedded in the rear surface of the thyroid gland. They secrete parathyroid hormone (PTH) a polypeptide of 84 amino acids. PTH increases the concentration of Ca2+ in the blood in three ways. PTH promotes
release of Ca2+ from the huge reservoir in the bones. (99% of the calcium in the body is incorporated in our bones.)
reabsorption of Ca2+ from the fluid in the tubules in the kidneys
absorption of Ca2+ from the contents of the intestine (this action is mediated by calcitriol, the active form of vitamin D.)
PTH also regulates the level of phosphate in the blood. Secretion of PTH reduces the efficiency with which phosphate is reclaimed in the proximal tubules of the kidney causing a drop in the phosphate concentration of the blood.
Hyperparathyroidism
Elevate the level of PTH causing a rise in the level of blood Ca2+ .Calcium may be withdrawn from the bones that they become brittle and break.
Patients with this disorder have high levels of Ca2+ in their blood and excrete small amounts of Ca2+ in their urine. This causes hyperparathyroidism.
Hypoparathyroidism
This disorder have low levels of Ca2+ in their blood and excrete large amounts of Ca2+ in their urine.