Physiology and Anatomy 1

• Proteins with carbohydrate chains
• Major effect of the carbohydrate connection is that it increases the biological half life considerably 
• Glycoprotein have a half life of hours instead of minutes

Glucocorticoids, Mineralcorticoids, Sex steroids

Because the steroids are highly lipid soluble, once they are synthesized the simply diffuse across the cell membrane and enter the interstitial fluid and the blood, where they are mainly transported bound to proteins.

Once they are released from the transport proteins, the hormones diffuse through the cell membrane of their target cells

1. Zona glomerulose
2. Zona fasciculata
3. Zona reticularis

Secretion of adrenocortical hormones by these 3 distinct zones

• Derivative of amino acids
• Mainly tyrosin: Catecholamines, thyroid hormones

• Synthesized in a series of enzymatic reaction
• Starting from the amino acid tyrosine and then serve as neurotransmitters and hormones
• Adrenalin and noradrenaline are formed in the adrenal medulla 

1. They are peripheral hormones (primarily adrenaline & noradrenaline)
2. They act as neurotransmitters in the nervous system (dopamine)

• Hormone-like messenger molecues
• They are not produced at a specific site but in many places through the body
• target cells ofter in vicitiny of the site of their secretion
• Important regularty molecules: Eicosanoids
• Most are linked to defense against damage and pathogens 

•  On the target cell membrane for peptide, protein and catecholamine hormones
• In the cytoplama for steroid hormones
• In the nucleus for thyroid hormones

• The first step of a hormone's action is to bind to specific receptors at the target cell
• The binding of hormones usually initiates a cascade of reaction in the cell
• Hormone receptors are large proteins and each receptor is usally specific for a single hormone

1. Intracellular recptors: for hydrophobic hormones (steroid, thyroid)
2. Extracellular receptors: for hydrophillic hormones (proteins, catecholamines) 

1. Enzyme-linked receptors
2. G-protein coupled receptors

• Steroid and thyroid hormones bind with protein receptors inside the cell
• The are lipid soluble so the cross the membrane and interact with receptors in the cytoplasma or nucleus
• The hormone receptor complex then binds with a promotor sequence of the DNA and activates or respresses transcription of specific genes and formation of mRNA 

• Combination of 4 subunits held together by  disulfide linkages 
• The recptor tyrosine kinase activity begins a cascade of cell phosphorylation steps that increases or decreases the activity of enzymes that mediate the effects of glucose, fate and protein metabolism 

Insulin binds to its receptor which starts a phosphorylation cascade that results in the translocation /insertion of the GLUT-4 transporter into the plasma membrane and the influx of glucose 

• Used for cellular signaling 
• Cell surface receptors
• Act like an inbox for messages in form of light, energy, peptides, lipids, sugars and proteins
• GCPRs interact with G-prteins in the plasma memrbane 

• When en external signaling molecule binds to a GPCR it causes a conformational change in the GPCR
• This triggers the interaction between the GPCR and the G protein
• G proteins can bind to GTP(active) and GDP(inactive) 

Self-regulating precess by which biological systems tend to maintain stabolity while adjusting to conditions that are optimal for survival. 

It involves keeping conditions whithin thighly regulated physiological tolerance limits

1. Negative Feedback: Occurs when response to a stimulus reduces the original stimulus
2. Occurs when response to a stimulus increases the original stimulus 

Negative feedback is the most common feedback loop. The system acts to reverse direction of change

• Endocrine gland
• Plays a central role in the regulation of neuroendocrine system of the body 
• Function: production and secretion of hormones 
• Structure:

1. Adenohypophysis (anterior) 
2. Neurohypophysis (posterior) 

• Contains endocrine cells that are activated by hormones released into pituitary blood vessles from small secretory neurons
• Endocrine cells are: ACTH, GH, FSH, TSH, LH
• hormones stimulate the secretion of other hormones from the anterior pituitary endocrine cells, which eventually enter the peripheral bloodstream 

• Nerve terminals from large secretory neurons of paracentricular hypthalamus. 
• These terminals release into pituitary bloodstream hormones like: Vasopressin, Oxytocin 

Hypothalamic hormones regulate anterior pituitary homones that in turn determine target gland secretion. 

--> To regulate hypothalamic and pituitary hormones 

• Made in the corticotroph cells of the anterior pituitary gland 
• Secreted in several intermitten pulses during the day into the bloodstream
• Levels of ACTH generally high in the morning and fall throughout the day (diurnal rhythm) 

Secretion of ACTH  is controlled by 3 inter communicating regions of the body: hypothalamus, pituitary gland and adrenal glands (HPA)

• When ACTH levels are low CRH hormones are released by the hypothalamus, which stimulates the pituitary gland to secrete ACTH 
• High levels of ACTH are detected by the adrenal glands which stimulate the secretion of Cortisol

The adrenocortical hormones are stroid molecules produced and released by the adrenal cortex. Secreion of adrenocortical steroids are controlled by ACTH.

1. Stimiulates contraction of the pregnant uterus 
2. Release of Oxytocin during breast feeding
3. Neurotransmitter related to the social binding, trust, love, sexual arousal
4. Control of energy balance: reduces food intake and body weight

Oxytocin receptors are GPCRs 

1. Conserve body water by reducing the loss of water in urine

Leptin is a peptide hormone made by adipocytes. It is a mediator of longterm regulation of energy balance, supressing food intake and inducing weight loss

• The more body fat, the more leptin is produced
• Binds to specific leptin receptors located through the central nervous system

• Lots of leptin tells the brain that plenty of fat is stored 
• Low levels tells the brain that fat stores are low and that we are at risk of starvation
• We eat --> body fat goes up --> leptin goes up --> we eat less and burn more 
• Obese individuals are resistent to leptin 

Ghrelin is a peptide hormone made by GI cells. Ghrelin regulates glucose homeostasis by inhibiting insulin secretion and regulating gluconeogenesis. It is made and released by cells in the upper part of the stomach. 

1. Stimulatory effects on food intake: increases hunger feeling 
2. Fat deposition 
3. Growth hormone release
4. Regulates energy balance 

Insulin is a hormone secreted within the pancreas in response to blood sugar levels. 

• Secreted by the beta cells of the pancreas
• Stimulus is high blood glucose
• Acts as a signal that triggers cells of the body such as fat and muscle cells to take up glucose for use as fuel
• Causes glucose to be converted into glycogen

• Is a hormone secreted within the pancreas
• Secreted in response to low blood sugar levels
• Increases the concentration of glucose in the blood

If you havent eaten in a while your blood glucose level falls, triggering the release of glucagon from another group of pancreatic cells (alpha cells) 

Insulin and glucagon work together