DIVE REFLEX + HOMEOSTASIS

What are the physiological responses to a dive?

HR changes and MAP is maintained/increases

How is HR changed?

Bradycardia follows breath holding (diving) via chemoreceptors in the carotid sinus and aortic arch stimulating parasympathetic activity and decreasing CO

How is MAP maintained?

Vasoconstriction in the periphery to direct more blood to hypoxia-sensitive organs (brain and heart) increases TPR which is due to increased sympathetic activity. This cancels out the decreased HR

What is the stimuli for the trigeminal/cranial nerve?

Facial immersion in water leading to a change in temperature, touch, and pressure

Where does the trigeminal/cranial nerve synapse?

Nucleus tractus solitarius in the medulla oblongata

Cell differentiation

The process where an unspecialised cell turns into a specialised cell

Gain

This is the effectiveness of a homeostatic system, the higher the better

Correction / Error

Requirements for negative feedback

Sensor, ability to compare to reference, sufficient gain, and effector mechanism

Body fluid compartments

ICV (2/3) + ECF (1/3)

Compartments of ECF

Interstitial fluid (3/4) + Plasma Volume (1/5) + Transcellular fluid (1/20)

High in Na⁺, Cl^-, Ca²⁺, and low K⁺ and proteins (some in PV)

BV

PV/(1-Hct)

Osmolarity of ICF

Low in Na⁺, Cl^-, Ca²⁺, and high in K⁺ and proteins

Na⁺/K⁺ ATPase

Active transport (2 K⁺ in and 3 Na⁺) and ubiquitous in every basolateral membrane of cells, contains α and β subunits, important in establishing a Na⁺ gradient

Other notable pumps

MDR transporters, ATP binding cassette, Na⁺/Glucose transporters, Na⁺/Ca²⁺ exchangers

Dissociation

A molecule dissolving into more than 1 ions will result in 1 mol = 1 x No. of ions

Hypotonic

Causes cell swelling and potentially lysis as osmolarity is higher in cells

Isotonic

No net water movement

Hypertonic

Causes cell shrinkage (crenation) as osmolarity is lower in cells

Absorptive function of small intestine

Non-electrolyte nutrients (proteins, fats, carbs, micronutrients, and vitamins), with H₂O and electrolytes (Na⁺, Cl^-, K⁺)

Secretory function of small intestine

Secretes HCO₃^- in the form of pancreatic bile

Secretory function of large intestine

Secretes HCO₃^- and K⁺

Absorptive function of large intestine

Na⁺, Cl^-, and H₂O

Anatomy of small intestines

Folded at 3 levels with a length of 6 m: Folds of Kerchring, villi and crypts of Lieberkuhn, microvilli

Anatomy of large intestines

Folded at 3 levels with a length of 2.4 m: Semiluminar folds, crypts but no villi, microvilli

Leaky epithelia

Paracellular pathway dominates (e.g. proximal tubule, small intestine)

Tight epithelia

Transcellular pathway dominates (e.g. collecting duct, urinary bladder) and can be under hormonal control

Na⁺ absorption

Uses the Na⁺ gradient and goes through Na⁺ channels or coupled transporters (Na⁺/Glucose x, Na⁺/aa x, Na⁺/H⁺ x which can be parallel with Cl^-/HCO₃^- x)

Cl^- absorption

Closely linked to Na⁺ absorption but if not then can be either paracellular or transcellular (this involves exchanging Cl^- and HCO₃^-)

Diarrhoea

Voluminous (small intestine origin) and small volume diarrhoea (large intestine origin)

Osmotic diarrhoea

Results from macronutrients malabsorption resulting in osmotic pressure being retained therefore water is retained (Lactose intolerance, Coeliac disease)

Secretory diarrhoea

Results from increased active secretion resulting in isosmotic fluid loss (E. coli, increased cAMP, cGMP, Ca²⁺)

Solvent drag

Dissolved solute is swept along with bulk movement of a solvent (water)

Systems regulating H⁺

Acid-base buffers in body fluids (seconds), respiratory centre (minutes), kidneys (hours - days but most powerful)

Bicarbonate buffers

Everywhere and fast but weak as pK is 6.1

Phosphate buffers

Exclusively in renal tubules but strong. Main elements are H₂PO₄^- and HPO₄^-

Protein

Buffers intracellular environments

Alveolar ventilation

Increased → Decreased CO₂ → Decreased H2CO₃ → pH increases (more basic). This happens when pH goes below 7.2

Decreased → Increased CO₂ → Increased H2CO₃ → pH decreases (more acidic)

Secretion of H⁺ in kidneys

Uses Na⁺/H⁺ x and bicarbonate is reabsorbed

Active secretion of H⁺ in kidneys

An H⁺ ATPase actively secretes it into the lumen where it is coupled by passive transport of Cl^- and bicarbonate is reabsorbed

Addition of new HCO₃^- in kidneys

Obtaining Na⁺ from Na₂HPO₄^- and exchanging it with H⁺ to form NaH₂PO₄ to get rid of H⁺ and creating new bicarbonate

Glutamine is split into 2HCO₃^- and 2NH₄⁺ which is then secreted by Na⁺/NH₄⁺ x

Hypokalemia

Increased P_CO2 → Increases H⁺ and decreased HCO₃^- → Decreased EFV → Increased Angiotensin II and Aldosterone

Hyperkalemia

Decreased P_CO2 → Decreased H⁺ and increased HCO₃^- → Increased EFV → Decreased Angiotensin II and Aldosterone