Anatomy, Homeostasis & Endocrine

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Anatomy

Definition: the branch of science concerned with the bodily structure of humans, animals and other organisms, revealed by dsisection.

Subdivided into...

  • Gross anatomy - examination without a microscope
  • Microscopic anatomy - histology - tissues, cytology - cells.
  • Developmental anatomy - changes from fertilised egg to adult
    • Embryology - changes from egg to foetus at 8th week in utero
  • Pathology - changes associated with disease
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Physiology

Definition: the branch of biology that deals with the normal functions of living organisms and their parts.

Subdivided into...

  • Cell physiology - functional interaction of cells
  • Systemic physiology - funcional interaction of organs which make a system
  • Pathological physiology - functional effects caused by disesase on organ or system
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Anatomical Position

Reference point for all anatomical nomenclature:

  • Upright posture
  • Head, eyes & toes forward
  • Arms by sides
  • Palms facing upwards
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Common Anatomical terms

  • Superior (cephalad) - toward the head
  • Inferior (caudad) - away from the head
  • Posterior (dorsal) - toward the back of the body
  • Anterior - toward the front of the body
  • Lateral - away from the midline of the body
  • Medial - toward the midline of the body
  • Internal - away from the surface of the body
  • External (superficial) - toward or on the surface of the body
  • Central - at or near the centre of the body or organ
  • Peripheral - external to or away from the centre of the body or organ
  • Distal - part of an extremity that is farther from the point of attachent to the trunk
  • Proximal - part of the extremity that is closer to the point of attachment to the trunk
  • Parietal - pertaining to the outer boundary of body cavities
  • Visceral - pertaining to the interal organs
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Organ systems

  • Skeletal system
  • Urinary system
  • Digestive system
  • Respiratory system
  • Lymphatic system
  • Cardiovascular system
  • Muscular system
  • Endocrine system
  • Nervous system
  • Intergumentary system
  • Male & Femal Reproductive system
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Homeostasis

Definition: Maintenance of a relatively constant internal environment.

The human body is constantly responding to internal and external factors in order to maintain relative stability. 

Homeostasis is vital to the whole body as a whole as well as each individual cell.

  • Claude Bernard (1813-1878) - consistency of internal environment is the condition for free life.
  • Internal environment - immediate surroundings of cells
    • intracellular fluid and interstital fluid provide the medium around the cells.
  • Appropriate cullular functioning depends on the constancy of internal environment
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Cellular Homeostasis

Cells must maintain a constant internal environment and must be able to reproduce themselves when needed by the body

Cells need ions, nutrients and various other substances to perform cellular activities.

Intracellular and extraceullular fluids must both be maintained in order to allow the cells to function correctly.

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Intracellular Fluid (Cytosol)

Found in the cytosol

Liquid inside cells

Futher separated by organelles, e.g. golgi, mitochondria

Ion concentractions are different to extracellular fluid concentration gradients

Other components: enzymes, calcium and proteins

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Homeostasis maintains...

Temperature

pH

CO2 & O2 levels

Waste products

Hormones

Nutrients

Electrolytes

Pressure

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Features of a Homeostatic System

Set Point - the normal value for a gvien variable

Stimulus - the change in the variable

Sensor - monitors the variable

Integrator - detects the change from the normal value

Effect - brings about the change to try and restore homeostasis

TYPES OF FEEDBACK:

Negative feedback - changes to the normal state triggers a response which aims to re-establish normal state (corrective mechanism). 

Positive feedback - the response does not attempt to restore normal state, but instead continues in the same direction.

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Internal Factors

There are a number of features within the internal environment that must be kept constant at all times:

  • Chemical constituents: glucose, ions, hormones
  • Osmotic pressure, i.e. relative amounts of water and solutes
  • Levels of O2 and CO2
  • Temperature

Elimination of wastes, e.g. nitrogenous waste from protein metabolism, environmental pollutants and toxic substances liberated by pathogens

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Glucose Homeostasis

Normal glucose levles after normal meal: 4-7mM

After heavy meal, glucose level rarely exceeds: 10mM

Blood glucose regulation:

2 hormones regulate blood glucose levels found in the pancreas:

Insulin - Glucose ==> Glycogen (decreases blood glucose levels)

Glucagon - Glycogen ==> Glucose (increases blood glucose levels)

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Blood Glucose Regulation

EXCESS GLUCOSE:

  • Change detected by B-cells
  • Increase in insulin secretion
  • Activates enzymes converting glucose ==> glycogen
  • Increases rate of glucose uptake
  • Levels return to normal

DEFICIENCY IN GLUCOSE:

  • Change detected by A-cells
  • Increase in glucagon secretion
  • Activates enzymes converting glycogen ==> glucose
  • Levels return to normal
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Role of the Liver & Pancreas

When glucose levels increase, less glucagon and more insulin is released by the pancrease and targets the liver.

When glucose levels decrease, less insulin and more glucagon is released by the pancreas and targets the liver.

The liver cannot respond properly to the body's needs without a functioning pancreas. 

Risk factors:

  • Age
  • Obesity
  • Diabetes
  • Gingivitis
  • Smoking
  • Chronic Alcoholism
  • Pancreatic Tumours
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Diabetes

Inability of islet of Langerhans to produce insulin:

  • increase in glucose concentration in plasma (hyperglycaemia)
  • glucose in the urine (glycosuria)

Treatment: controlled by regular injection of insulin

Having diabetes increases risk of:

  • Cardiovascular disease
  • Hyperlipidaemia
  • Neuropathy
  • Erectile dysfunction
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Thermoregulation

Humans maintain fairly constant internal temperatures of 35 - 40 degrees.

Temperature is controlled by the thermoregulatory centre located in the hypothalamus.

Temperature detection:

  • Receptors in the hypothalamus
  • Receptors in the skin
  • Sweating
  • Vasodilation
  • 37.5 degrees
  • 36.5 degrees
  • Vasoconstriction
  • Shivering

Under stress, 48% of blood flows to the skin for heat loss, whereas in normal blood flow, only 4% of blood flows to the skin for heat loss.

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Thermoregulation - High temp

Stimulus: Core temperature (above 37.5 degrees)

Sensor: Temperature receptors in skin & hypothalamus

Communication: Afferent nerves

Control Centre: Thermoregulatory centre in hypothalamus

Communication: Efferent nerves

Effector: Dilation of blood vessels in skin, increased sweat rate

Decrease in Core Temperature

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Thermoregulation - Low temp

Stimulus: Core temperature (below 36.7 degrees)

Sensor: Temperature receptors in skin & hypothalamus

Communication: Afferent nerves

Control Centre: Thermoregulatory centre, hypothalamus

Communication: Efferent nerves

Effector: Constriction of blood vessels in the skin, decreased sweat rate, increased metabolism, shivering

Increase in Core Temperature

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Positive Feedback - Labour

Parturition (childbirth)

Stimulus: pressure of foetal head on cervix

Sensor: pressure receptors in the cervix

Communication: afferent nerves

Control Centre: hypothalamus, posterior pituitary gland

Communication: oxytocin in the blood

Effector: contraction of uterus

Process of contractions continue until the baby is born.

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The Endocrine System

  • The second co-ordinating and integrating system of the body and tramsits signals using chemical signals (hormones).
  • 4 actions:
    • Maintain homeostasis
    • Control storage and utilisation of energy
    • Regulation of growth, developments and reproduction
    • Respond to environmental stimuli
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Hormones

Specific chemical messenger molecules that regulate the activity of cells or organs in the body.

Synthesised and secreted by cells in endocrine glands - 1st messenger

Essential for every activity in life, including processes of digestion, metabolism, growth, reproduction and mood contol.

Stimulus ==> Receptor ==> Hormone ==> Effector ==> Response

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Classes of Hormone

Based on their chemical structure...

Steroid hormones: includes the sex hormones all of which are lipids made from cholesterol

Amino acid derivatives: (like adrenaline) which are derived from amino acids, especially tyrosine

Peptide hormones: (like insulin) which is the most numerous/diverse group of hormones

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Intracellular Signalling

Four types:

Autocrine

Paracrine

Endocrine

Synaptic

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Types of Signalling

Autocrine signalling - signalling and target cell are the same.

e.g. Interleukin-1 (cytokine) released from monocytes to target monocytes (positive feedback)

Paracrine signalling - signalling cell and target cell are close together.

e.g. Fibroblast Growth Factor family - stimulates cell division/proliferation (limb development)

Synaptic signalling - signal travels through neurones and transmitted across a synaptic cleft. 

e.g. Chemical messenger acetylcholine travels through synaptic cleft to transmit impulses

Endocrine signalling - signal travels through bloodstream to target cell. 

e.g. Aderenaline is secreted from the adrenal glands into the blood.

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Main endocrine glands & their hormones

  • Pineal gland (melatonin) - affects reproductive development and daily physiologic cycles
  • Pituitary gland (growth hormone, ADH, gonadotrophins) - growth hormones control growth of bones and muscles, ADH increases reabsorption of water in kidneys and gonadotrophins control development of ovaries and testes.
  • Thyroid gland (thyroxine) - controls rate of metabolism and rate that glucose is used up in respiration and promotes growth.
  • Adrenal gland (adrenaline) - prepares the body for emergencies increases heart rate and rate of depth of breathing, raises blood sugar level so more glucose is available for respiration, diverts blood from gut to limbs.
  • Pancreas (insulin & glucagon) - insulin converts excess glucose into glycogen in liver and glucagon converts glycogen back to glucose in the liver.
  • Ovaries (oestrogen & progesterone) - oestrogen controls ovulation and secondary sexual characteristics and progesterone prepares the uterus lining for receiving an embryo.
  • Testes (testosterone) - controls sprerm production and secondary sexual characteristics.
  • Thymus (thymosin) - promotes production and maturation of white blood cells
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Pituitary Gland

  • Change detected in the hypothalamus
  • Posterior pituitary gland releases ADH 
  • Increases reabsorption in the kidney, fluid reabsorbed depends on the body's needs.

If this process goes wrong..

Diabetes Insipidus:

  • Increases urination > 3L / 24hrs
  • Increased fluid intake
  • 1:25000 in the USA
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Pancreas

The pancreas is responsible for secreting hormones that regulate blood glucose levels using insulin and glucagon. However if this process goes wrong, a person could develop Diabetes Mellitus type 1 or Diabetes Mellitus type 2

Type 1:

  • insulin-producing cells are destroyed
  • the body is unable to produce insulin
  • glucose cannot be used for energy and so proteins and fats are broken down which can cause weight loss
  • glucose ends up passing into the urine
  • treated with insulin injection

Type 2:

  • there is not enough insulin or the insulin produced isn't working/being recognised
  • glucose builds up in the blood
  • treated with a healthy diet and increased physical activity
  • medication/insulin often required
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Adrenal Glands

  • Adrenal medulla produces...
    • Catecholamines
    • Adrenaline
  • Adrenal Cortex produces...
    • Glucocorticoids - Cortisol
    • Mineralcorticoids - Aldosterone
    • Androgens - Testosterone
  • If the adrenal glands are not working properly...
    • Symptoms:
      • Fatigue, lassitude, malaise, weakness, anorexia
      • Postural dizziness, syncope
      • Gastrointestinal: nausea, vomiting, abdominal pain, diarrhea, constipation
      • Decreased libido
    • Signs:
      • Weight loss
      • Hyperpigmentation
      • Hypotension
      • Thinning of axillary and pubic hair
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Thyroid Gland

  • Produces both Thyromine and Triiodothyronine
    • metabolic activity
    • control of growth
    • nervous system development
  • Two lobes of the thyroid gland - very rich blood supply.
  • TSH from pituitary stimulates release of thyroid hormones
  • Hyperthyroidism symptoms:
    • weight loss
    • increased appetite
    • irritability/behaviour change
    • restlesness
    • tremor
    • heat intolerance
  • Hypothyroidism symptoms:
    • tiredness
    • weight gain
    • cold interolance
    • anorexia


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