Endocrine System Flashcards
Define homeostasis and allostasis.
The bodies ability to regulate fluids and temeperature to optimise its function.
Allostasis is the idea that the body predicts effects before they happen and adjusts accordingly.
Discuss what regulates body temperature and possible problems with this.
Humans are able to maintain a steady core temperature despite changes to external environments. The volume of the core can expand in warm conditions and shrink in cool conditons. Heat is produced by metabolic processes in the body.
- Thermoreceptors in the tissues record changes in temperature and send sensory afferents to the hypothalamusn (2 centres for cold and hot response). Acts on multiple effector systems.
- Change in muscle activity: shivering, adrenergic pathway with hypothalamus (non-voluntary somatic).
- Brown fat metabolism: important in newborns, an increase in epinephrine and thyroid hormones causes metabolism of brown adipose.
- behavioural
- blood flow to skin (constriction and dilation): adrenergic efferents from the hypothalamus. Can override the medulla.
- Not enough in extreme temperatures
- Fever- Pyrogens from microorgansim reset hypothalamus set point by the activation of prostglandins. Can trick the body into producing excessive heat, Aspirin blocks.
- Hyperthermia can be induced by exercise
- Excess thyroid hormones or epinephrine can cause hyperthermia.
Discuss the role for the hypothalamus in homeostasis.
The hypothalamus acts as a controll centre for homeostasis. It produces several hormones which are important for regulation of temperature and fluid retention. An example would be its action on the pituitary gland. ADH is released from the posterior pituitary (neurohormone acts on kidneys to increase fluid retention in the kidneys. Recruits aquapores that insert into the kidney tubules). On the posterior pituitary there is no portal system connecting the two (neurons whos bodies are in the hypothalamus), signals the release of neurohormones
It controls the anterior pituitary through releasing and inhibiting hormones that reach the pituitary via a capillary network. The anterior pituitary releases hormones such as TSH (TRH from hyp), GH (GNRH from hyp), (GnRH)LH, FSH, Prolactin (PIH, PRH).
Explain the anatomy of the kidneys and adrenal glands including their location within the abdomen.
Kidneys are located in the posterior portion of the abdominal cavity. They are bilateral bean shaped organs. They are paired structures which sit retroperitoneally in the abdomin. Kidneys sit roughly in the region of T12- L3 but right kidney sits slightly lower due to the liver. The kidneys are incased in several layers of fat and fascia. The innermost layer is the renal capsule. The kidneys can be split functionally between the outer cortex and the inner medulla. The cortex extends into the medulla via triangular structures known as renal pyramids. The apex of the pyramid is known as the renal papilla. The renal papillae are associated with structures known as minor calyx which lead into major calyx. The calices collect urine from the pyramids to be transported to the ureter via the renal pelvis. Pyramids contain functional units known as nephrons. Blood supply via the renal arteries and drainage by the renal veins. (renal helum, interlobar arteries> arcuate arteries> interlobular). Pelvic Kidney- In utero, the kidneys develop in the pelvic region, and ascend into the abdomen. Occasionally, one of the kidneys can fail to ascend, and remains in the pelvis, at the level of the common iliac artery.
The adrenal glands sit directly inferior to the kidneys in the renal fascia. Contain outer capsule> cortex (embryonic mesodemr)> medulla (ectodermal neural crest cell).
Compare the renal and endocrine anatomy between males and females.
The ureter transports urine to the bladder which exits as the urethra through the penis in males and the perineum in females. The main difference in endocrine anatomy between males and females lies in the sex organs. Women contain ovaries which produce oestrogen and progesterone and also utilise oxytocin and prolactin for breast development and lactation. The male sex organs are the testies which produce testosterone.
Describe the anatomy of the key endocrine organs including the hypothalamus, pituitary, thyroid and pancreas.
The hypothalamus is a subcortical brain structure located anterioposteriorly from the thalamus.
The pituitary consists of 2 lobes which suspend from the base of the brain via a pituitary stock. It sits in small indentations in the sphenoid bone known as the sella turcica.
The thyroid gland is located posterior to the sternothyroid and sternohyoid muscles in the neck. It consists of 2 lobes joined by an isthmus which wraps around the cricoid cartilage. Vasculature- superior and inferior thyroid arteries. Some individuals also have thyroide ima artery. Drainage via a venus plexus which leads into the internal jugular veins.
Pancreas- Located posteriorly to the stomach, duedonem lies anteriorly and laterally, Transverse mesocolon – Attaches to the anterior surface of the pancreas
Common bile duct – Descends behind the head of the pancreas before opening into the second part of the duodenum alongside the major pancreatic duct through the major duodenal papilla
Spleen – located posteriorly and laterally. The lienorenal ligament is formed from peritoneum and connects the spleen to the tail of the pancreas. The pancreatic duct runs the length of the pancreas and unites with the common bile duct, forming the hepatopancreatic ampulla of Vater. This structure then opens into the duodenum via the major duodenal papilla.
Discuss the function of the key endocrine organs.
Hypothalamus- hormone secretion which acts on various systems
Pituitary- also hormone synthesis- controlled by hypothalamus
Thyroid- secretes thyroid hormones
Pancreas- secretes insulin and glucagon
Define the componants of an endocrine system and understand how they interact to cause physiological effects.
An endocrine system consists of cells which secrete hormones which are released into the blood stream and have an action on cells elewhere in the body. They consist of endocrine cells, their hormones/ neurotransmitters and the tissues that the act upon. Hormones can bind to surface receptors on cells or bind to receptors on the nuclear membrane. They normally cause a change in gene expression (production of proteins).
Define hormones on the basis of structure.
Peptides: Polypeptide chains which are normally synthesised in the rough endoplasmic reticulum as preprohormones which require the removal of subunits in order to be in their active state (insulin). Stored in vessicles.
Tyrosine derivatives: derived from tyrosine groups (thyroid hormones). They can be both hydrophobic and hydrophilic and therefor have different mechanisms.
Steroids: large hydrophobic proteins that are derived from cholesterol. They are important for growth, sexual characteristics and stress response. Can freely diffuse through the cellular membrane and bind to nuclear receptors. They are released upon their production attatched to carrier proteins.
Discuss the simple principles of feedback mechanisms in the control of hormone secretion using the HPA- axis as an example.
Feedback mechanisms involve a control centre, an effector, a controlled mechanism and a feedback to the control centre. An example would be the HPA axis. The hypothalamus acts as a control centre. Hypothalamus sends CRH to the anterior pituitary> Anterior pituitary (effector) sends ACTH to the Adrenal cortex> Adrenal cortex releases cortisol (response). The increase in cortisol is detected which feeds back to both the pituitary and hypothalamus to decrease the release of effector hormones.
Discuss insulin production and action.
Insulin is produced in the B islet cells of the liver. Its primary function is to reduce glucose levels in the blood. Insulin binds to membrane-bound receptors on target tissues and causes proteins in the membrane to become phosphorelated. Inreases the number of transport proteins for glucose and amino- acids. Insulin and receptor then enters the cell by endocytosis. It causes the conversion of excess glucose into glycogen for storage in the liver and other tissues or converted into lipids in adipose tissues.
Explain ATP synthesis and glycolosis.
Carbohydrate metabolism
Glycolysis- Phosphorylation of ATP forms a glucose intermediate. This is rearanged to form a fructose intermediate. A second ATP then phosphorelates the fructose intermediate forming a biphosphate intermediate. The sugar is cleaved into 2 3C molecules. 2x NADH is produced by the oxidation of the molecules by NAD+. 2 ATP molecules are produced in the final step per molecule creating a net gain of 2 ATP. The molecules are converted to pyruvate in this step which can travel on to the citric acid cycle or be converted into lactic acid in the absence of O2.
Describe carbohydrate/ glucose homeostasis.
High glucose levels leeds to the production of insulin from B islet cells and in cases of low insulin glucagon is relased from a- islet cells. Insulin works primarily on the liver
Describe what diabetes mellitus is.
It is either the result of inadequate production of insulin (type 1) or the inadequate response to insulin (type 2).
Type 1 is the result of autoimmune response towards pancreatic islet cells. Type 2 usually develops in older individuals with high sugar diets. The over stimulation of insulin receptors results in lower sensitivity (reduced numbers of receptors) which makes tissue response to insulin considerably lower. This in turn can cause an increase in blood glucose.
Discuss how diabetes effects the body.
An increase of glucose in the blood which causes it to be converted into lipids for storage (impaired), increased urine production and thirst is common and can lead to hyperosmolity of blood and dehydration of cells. Lethargy, fatigue and periods of irritability. Type 1 tend to undergo sudden spikes and drops in blood glucose due to reduced control hormones.
