Endocrine System and High Altitude Physiology

Human Endocrine System and Homeostasis

• Human mechanisms facilitate responses to the external environment ensuring a stable internal state.
• The nervous, endocrine, and immune systems cooperate to maintain stability and protect the organism.

Nervous System Response

• A rapid response to stimuli characterizes as a key trait.
• Electrical impulses and neurotransmitters are employed.

Endocrine System Response

• Endocrine glands distributed through the body control the response.
• The response is slower but has a long-lasting effect.
• Specific hormones are produced and released by endocrine glands into the bloodstream.
• Effector organs are targeted for response initiation.
• Endocrine disorders can arise from over- or under-stimulation of endocrine organs.

Key Terminology

Endocrine system

• The endocrine system is responsible for chemical coordination and regulation of various bodily activities.

Homeostasis

• This is maintenance of a stable internal environment (blood and tissue fluid) within the body.

Hormones

• Acting as chemical messengers, hormones travel in the bloodstream with effects elsewhere in the body.

Negative feedback

• Changes or imbalances in the internal environment are detected and balance is restored in the human body.

Osmoregulation

• Regulation of water balance occurs in the internal environment.

Osmotic pressure

• This is the concentration of solutes in a solution determining water gain or loss by a cell.

Antagonistically

• Working in opposite ways, one hormone increases a substance while the other one decreases it, e.g., insulin and glucagon.

Thermoregulation

• Body temperature is controlled to keep it close to roughly 37°C.

Endothermic

• Endothermic relates to an organism that generates heat internally through metabolic processes to maintain a constant body temperature.

Vasoconstriction

• Narrowing of blood vessels is observed.

Vasodilation

• Widening of blood vessels is observed.

Evaporation

• Heat is lost when sweat changes into water vapor on the skin's surface.

Conduction

• Heat is transferred between objects in direct contact.

Convection

• Warm air rises and is replaced by cooler air

Radiation

• Heat is transferred between two objects not in contact

Homeostasis

• This is an organism's tendency to regulate internal conditions using feedback controls to stabilize health regardless of external changes.

Secretory Glands

• Mammals produce secretions via exocrine and endocrine glands.

Exocrine Glands

• Contain ducts.
• Secretions are released into a cavity or onto a surface.
• Examples include salivary glands (saliva) and sweat glands (sweat).

Endocrine Glands

• Ductless.
• Hormones are secreted directly into the bloodstream.
• Examples include the pituitary (ADH), thyroid (TSH), and pancreas (insulin).
• The pancreas is both an exocrine and endocrine gland secreting digestive enzymes to the small intestine and insulin/glucagon into the bloodstream.

Endocrine Glands

• Endocrine glands secrete hormones that are transported to target sites via the bloodstream.
• Hormones interact sequentially producing a common effect or working antagonistically.
• Hormones are organic messengers with most as proteins or steroids (lipids) needed in small amounts.
• Hormones trigger prolonged responses compared to nerve responses.
• Hormone secretion disorders may result from oversecretion or undersecretion.
• Basic hormone functions: Reproduction, growth, development, maintenance of internal environment, regulation of metabolism

Hypothalamus and Pituitary Gland

• The hypothalamus is a small brain area linked to the pituitary gland.
• The hypothalamus produces important hormones and links the nervous and endocrine systems.
• The hypothalamus regulates vital body functions and produces antidiuretic hormone (ADH).

Hormone Functions

Hypothalamus

• ADH (vasopressin): promotes water re-absorption in kidneys and protects against dehydration.

Pituitary Gland (anterior lobe)

• TSH: stimulates thyroid growth and thyroxin secretion.
• FSH: stimulates follicle development in ovaries, estrogen production, and development of ova. It also stimulates sperm production in the testes.
• LH: stimulates ova maturation and ovulation in ovaries, and testosterone production in testes.
• Prolactin: stimulates milk production and secretion by mammary glands.
• GH: stimulates the growth of long bones and skeletal muscles.

Other Important Endocrine Glands

• Adrenal glands
• Ovaries
• Testes
• Pancreas
• Thyroid glands
• All endocrine glands are essential for healthy metabolism.

Adrenal Glands

• The adrenal glands are triangular glands on top of each kidney, having a medulla and outer cortex.
• The hormones adrenalin and aldosterone are secreted from the adrenals.

Functions

Adrenalin

• Increases heart rate and blood supply to cardiac muscles.
• Stimulates the liver to convert glycogen into glucose.
• Increases blood supply to skeletal muscle.
• Stimulates pupil dilation
• Decreases blood supply to less vital organs (digestive system and skin).
• Increases breathing rate
• Increases metabolic rate

Aldosterone

• Regulates blood salt (sodium, potassium) concentration; works with ADH.

Reproductive Glands

• The hormones released play a vital role in reproduction and the development of secondary sexual characteristics during puberty.
• Ovaries in females are stimulated by FSH from the pituitary gland.
• Ovaries release estrogen and progesterone.
• Leydig cells in the testes of males secrete testosterone, which stimulates sperm production and maturation.

Hormone Functions

Oestrogen

• Promotes thickening of the endometrial wall.
• Promotes development of female secondary sexual characteristics at puberty and fertility.

Progesterone

• Promotes further thickening and vascularization of the endometrial wall.
• Maintains embryo implantation during pregnancy.

Testosterone

• Stimulates development of male sex organs and secondary sexual characteristics during puberty.
• Promotes maturation of sperm.

Negative Feedback

• Negative feedback involves two hormones; one stimulates an increase in another, which then inhibits the first to restore balance.

Sequence of events

• An imbalance is detected by the receptors
• The control center is stimulated and responds
• A message is sent to the target organs, the effectors
• The effector responds by opposing the imbalance and restores balance.

Homeostatic Control of the Internal Environment

• Tissue fluid surrounds cells constituting the internal cellular environment.
• Conditions within cells depend on the internal environment's conditions.
• The human body ensures homeostasis when faced with external and internal changes.
• Without it, organs, systems and organisms may be negatively affected.

Key variables with homeostatic mechanisms:

• Maintenance of water, salt, and glucose levels
• Regulation of carbon dioxide concentration and body temperature
• Regulation of thyroxin levels

Homeostatic Controls

• Proper control of the above factors is necessary.
• All metabolic reactions require a balance of water and salt in tissue fluid
• Dissolved salts in tissue fluid determine osmotic pressure, affecting water balance
• Gases affect respiration and blood pH.
• Glucose concentrations ensure energy levels and metabolism.
• Enzyme activity as related to the enzymes denaturation is influenced by variance in normal body temperature.

Osmoregulation

• Body metabolism depends on the maintenance of water balance.
• The homeostatic control of water and salt levels in blood and tissue is achieved by osmoregulation via a feedback system

Decreased water levels (dehydration)

• Is caused by excessive exercise, heat, and sweating, or decreased water intake.
• Hypothalamus osmoreceptors detect low water levels.
• The pituitary releases ADH to the kidney, which increases water reabsorption.
• The blood becomes diluted, and concentrated urine is excreted.

Increased water levels (overhydration)

• Is caused by cooler temperatures, little exercise, and an excessive water intake.
• High water levels are detected by the hypothalamus.
• The pituitary releases less ADH, decreasing water reabsorption.
• More water is lost, and diluted urine is excreted.

Salinity Regulation

• Solutes affect the osmotic pressure in blood and tissue fluids (glucose, salts).
• Sodium and potassium ions are regulated in negative feedback

Low salt levels

• Kidney receptors detect decreased sodium ions.
• Adrenal glands secrete aldosterone which stimulates sodium reabsorption into the blood and decreases urine excretion.

High salt levels

• Kidney receptors detect increased sodium ions.
• Adrenal glands stop aldosterone secretion.
• Sodium is not reabsorbed and is excreted more in urine.

Carbon Dioxide Regulation

• Carbon dioxide affects blood pH.
• Carbon dioxide dissolves in water creating carbonic acid which lowers blood pH.
• High carbon dioxide means low blood pH and it influences enzyme activity.

Process

• High carbon dioxide leads to low pH in the carotid artery where chemoreceptors are stimulated
• Impulses are sent to the medulla oblongata.
• Breathing targets heart muscles and intercostals
• Diaphragm and intercostals contract deeper, also increasing heart rate
• Carbon dioxide moves to the lungs and exhales.

Blood Glucose Regulation

• Carbohydrates are short-term energy storage and broken down to release energy.
• The pancreas secretes insulin and glucagon to regulate blood glucose antagonistically

High blood glucose

• Elevated levels are detected in the Islets of Langerhans in the pancreas.
• The Islets respond by secreting insulin into the bloodstream.
• Insulin transports to the effector, which is the liver.
• Enzymes in the liver catalyze conversion of excess glucose into glycogen.
• Glucose stored in the storage carbohydrate then goes back to normal

Low blood glucose

• Decreased glucose levels detected in the Islets of Langerhans in the pancreas.
• Glucagon is released from the liver to the bloodstream
• The effector organ turns glycogen into glucose.
• Glucose is released into the blood.
• Glucose levels are increased to normal.

Thyroxin Levels Regulation

• The essential hormone thyroxin stimulates metabolism.
• The basal metabolic rate is the rate at which a body uses energy when resting.
• Iodine helps the production of good thyroxin levels

Thyroxin's role:

• stimulates increased metabolic rate
• plays a key role in heart and digestive function
• assists skeletal and brain development
• maintains muscle tone

Process of thyroxin

• The hypothalamus and pituitary in brain control normal secretion of hormones.

With low levels of thyroxin

• Below normal hormone levels stimulate the pituitary gland, causing secretion of TSH.
• TSH is transported to the thryoid gland where it stimulates thyroxin
• The hormone level then goes back to normal feedback loop.

Endocrine System Disorders

• Hormone secretion disruptions affect homeostasis.
• Hyposecretion is too little hormone.
• Hypersecretion is too much hormone.
• The individual is diagnosed with an endocrine problem upon continued disorder.

Pituitary Gland Disorders

• Acromegaly is the hypersecretion of GH after puberty, resulting in the enlargement of hands, feet, forehead, jaw, and nose.
• Dwarfism is the hyposecretion of GH during childhood, resulting in the well-proportioned but short stature and delayed puberty, for example.
• Gigantisim is hypersecretion of GH in childhood. long bones and connective tissue grows very fast which potentially causes person to grow up to 2.1 to 2.5 m causing high blood pressure.

Thyroid Gland Disorders

• Hyperthyroidism is excess thyroxin production and hypothyroidism from continued low levels of thyroxin

Grave’s disease

• Is the autoimmune disease which causes the antibody to attack receptors on the cells of thyroid gland causing the thyroid gland to produce excess thyroxine hormone T4.

Symptoms of Grave's Disease

• Bulging eyes
• Weight loss
• Fast metabolism

Goitre

• Goiter is elevated thyroid activity
• A negative effect of goiter is an increased metabolic rate and cardio-vascular activity with anxiety and swollen neck.

Cretinism

• It's caused by lack of the hormone thyroxine and the characteristics are a physical with mental retardation.

Myxoedema

• Is cause of underactive thyroid gland in adulthood with characteristics of mental and physical tiredness with low metabolic rate causing thickening and swelling in the skin.

Pancreas Disorders

• Diabetes describes continually high glucose levels
• Diabetes mellitus is a disease associated with high blood sugar levels.

Diabetes Long-term effects

• Blood vessel damage which eventuallly leads to circulatory problems and multiple organ damage.
• Impaired wound healing and blindness are observed

Diabetes treatments

• Type 1 diabetics might inject insulin as a treatment.
• There are insulin pump that help control glucose effectively.
• Type 2 diabetics can control insulin levels by diet, weight loss and exercise.

Type 1 diabetics

• Pancreas is not producing hormone insulin which helps to control glucose levels.

Type 2 diabetics

• Body is unavailable to help control glucose levels

Thermoregulation in mammals

• Endotherms maintain a constant body temperature independent of the birds and mammals.
• Humans maintain near 36,8°C.
• Metabolism continues if temperatures are stable.
• Increased rate causes enzyme denaturation.
• Body controls internal core temperature to regulate the surrounding environment.

How the Human Skin Thermoregulates

Mechanisms

• Evaporation
• Radiation
• Conduction
• Convection

How the body transmits the temp

• Body's thermoreceptors transmit messages to regulate center.
• Responses to environment that regulates the core to maintain constant.
• Transmitting heat, adding clothes, and shivering,

In a hot environment

• body increases the temperature
• Warm blood passes the hypothalamus
• Sent to vessels of glands and vasodilatation (more heat lost), causes air by regulation
• sweat gland produces more sweat causes a basal metabolic rate

In a cold environment

• Decreases body temperature where blood passes slightly
• Impulses sent to glands to the vessels which constricts the vessels (less air lost)
• Less metabolic rate increase and the thyroid increases skeletal muscle which involuntary produces heat

Explore the functions of the hypothalamus, pituitary gland, and adrenal gland. Learn about hormones like insulin, glucagon, and ADH, and their roles in blood sugar regulation and water reabsorption. Discover the challenges of high-altitude climbing, including hypoxia and strategies for acclimatization and heat conservation.