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Unit 1 of 3 · B.Sc MLS Sem 3

Unit 1: Body fluids and the digestive system

Human Anatomy & Physiology-II notes · PTU syllabus (BMLS303-18)

3 min read7 topics10 exam questions
On this page
  1. Unit summary
  2. Body fluids and total body water
  3. Electrolytes and their functions
  4. Fluid balance and imbalances
  5. Organisation of the digestive system
  6. Digestive glands and accessory organs
  7. Physiology of digestion
  8. Structure and functions of the liver
  9. Key terms
  10. Quick revision
  11. Important questions

Unit summary

Body fluids and digestion keep cells supplied with water and nutrients. This unit covers body fluid compartments, total body water, fluid and electrolyte balance and imbalance, the organisation of the digestive system, the structure and function of its organs and glands, the digestion of carbohydrates, lipids and proteins, and the liver.

After this unit you can

  • Describe body fluid compartments and electrolyte functions
  • Explain fluid and electrolyte imbalances
  • Describe the organs and glands of the digestive system
  • Explain digestion and the functions of the liver

PTU syllabus topics

  • Types of body fluid
  • total body water
  • fluid balance and homeostasis
  • electrolytes and their function
  • electrolyte and fluid imbalance
  • digestive system organization
  • accessory organs
  • structure and function of mouth/tongue/teeth/oesophagus/pharynx/stomach/intestine/rectum/anus
  • digestive glands
  • physiology of carbohydrate/lipid/protein digestion
  • liver structure and function
ProcessPath of digestion
  1. 1

    Mouth

    Salivary amylase starts on starch

  2. 2

    Oesophagus

    Peristalsis

  3. 3

    Stomach

    Pepsin and HCl digest protein

  4. 4

    Small intestine

    Bile, pancreatic enzymes; absorption

  5. 5

    Large intestine

    Water absorbed

  6. 6

    Rectum and anus

    Elimination

1

Topic 1

Body fluids and total body water

  • Total body water is about 60% of body weight in adult men (about 50% in women, 75% in newborns).
ClassificationBody fluid compartments
Total body water (about 42 L in a 70 kg man)

  • Intracellular fluid

    Two-thirds (about 28 L)

  • Extracellular fluid

    One-third (about 14 L)

  • Interstitial fluid

    About 11 L — around cells

  • Plasma

    About 3 L

  • Transcellular fluid

    CSF, synovial, pleural, peritoneal fluids

ComparisonMajor electrolytes
Extracellular
Intracellular

Main cation

Sodium (135–145 mmol/L)

Potassium (about 150 mmol/L)

Main anion

Chloride, bicarbonate

Phosphate, proteins

2

Topic 2

Electrolytes and their functions

Key termsElectrolyte functions
Sodium
Extracellular volume and osmolality; nerve impulses
Potassium
Resting membrane potential; heart rhythm (normal serum 3.5–5.0 mmol/L)
Chloride
Osmotic balance, gastric HCl
Bicarbonate
Acid–base buffer
Calcium
Bones, clotting, muscle contraction
Magnesium and phosphate
Enzymes, ATP, bones
3

Topic 3

Fluid balance and imbalances

  • Balance: intake (drink, food, metabolic water about 2.5 L/day) equals output (urine, sweat, breath, faeces). Controlled by thirst, ADH (water retention) and aldosterone (sodium retention).
ComparisonFluid and electrolyte disorders
Cause
Features

Dehydration

Vomiting, diarrhoea, burns, low intake

Thirst, dry mucosa, low BP, high PCV and urea

Oedema and overload

Heart, kidney or liver failure; low albumin

Swelling, breathlessness

Hyponatraemia (Na below 135)

Water excess, SIADH, diuretics

Confusion, seizures

Hypernatraemia (Na above 145)

Water loss

Thirst, confusion

Hypokalaemia (K below 3.5)

Diarrhoea, diuretics

Weakness, arrhythmias

Hyperkalaemia (K above 5.5)

Kidney failure; haemolysed sample (false)

Dangerous arrhythmias

4

Topic 4

Organisation of the digestive system

ProcessAlimentary canal
  1. 1

    Mouth

    Teeth chew; tongue mixes; saliva starts starch digestion

  2. 2

    Pharynx and oesophagus

    Swallowing; peristalsis

  3. 3

    Stomach

    Stores and churns food; HCl and pepsin

  4. 4

    Small intestine

    Duodenum, jejunum, ileum — digestion and absorption; villi

  5. 5

    Large intestine

    Caecum, colon — water and salt absorption

  6. 6

    Rectum and anus

    Stores and expels faeces

  • Wall layers: mucosa, submucosa, muscularis externa, serosa.
Key termsTeeth
Incisors
Cutting
Canines
Tearing
Premolars and molars
Grinding
Dentition
20 milk teeth; 32 permanent teeth
5

Topic 5

Digestive glands and accessory organs

ComparisonDigestive glands
Secretion
Function

Salivary glands (parotid, submandibular, sublingual)

Saliva with amylase and mucus

Starch digestion, lubrication

Gastric glands

HCl (parietal cells), pepsinogen (chief cells), intrinsic factor, mucus

Protein digestion, kills microbes, B12 absorption

Pancreas

Amylase, lipase, trypsinogen, bicarbonate; insulin and glucagon (endocrine)

Digestion of all foods; neutralising acid

Liver and gall bladder

Bile (salts, pigments)

Fat emulsification

Intestinal glands

Disaccharidases, peptidases

Final digestion

6

Topic 6

Physiology of digestion

ComparisonDigestion of nutrients
Enzymes
End products

Carbohydrates

Salivary and pancreatic amylase; maltase, sucrase, lactase

Glucose, fructose, galactose

Proteins

Pepsin, trypsin, chymotrypsin, peptidases

Amino acids

Lipids

Bile salts emulsify; pancreatic lipase

Fatty acids and monoglycerides → chylomicrons

  • Absorption occurs mainly in the small intestine through villi and microvilli, which give a huge surface area.
7

Topic 7

Structure and functions of the liver

  • The largest gland (about 1.5 kg) in the right upper abdomen; made of hepatic lobules with hepatocytes arranged around a central vein and portal triads (portal vein, hepatic artery, bile duct); Kupffer cells line the sinusoids.
Key termsFunctions of the liver
Metabolism
Glycogen storage, gluconeogenesis, lipoproteins, urea formation
Synthesis
Albumin, clotting factors, bile
Detoxification
Drugs, alcohol, ammonia
Storage
Glycogen, vitamins A, D, B12, iron
Excretion
Bilirubin in bile
Defence
Kupffer cells remove bacteria
  • Liver function tests: bilirubin, ALT, AST, ALP, total protein and albumin, PT/INR.

Key terms

Total body water
Water content of the body, about 60% of weight
Electrolyte
Ion in body fluids conducting electricity
ADH
Hormone causing water retention by the kidneys
Villi
Finger-like projections increasing intestinal absorption
Hepatic lobule
Structural unit of the liver

Quick revision

  • ICF two-thirds, ECF one-third; Na⁺ outside, K⁺ inside.
  • Electrolyte roles; fluid balance; ADH, aldosterone.
  • Dehydration, oedema, Na and K disorders.
  • Parts of the gut; teeth; glands and secretions; digestion of nutrients.
  • Liver structure and functions; LFTs.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.What percentage of body weight is water?
  2. Q2.Name the main intracellular cation.
  3. Q3.Give two causes of dehydration.
  4. Q4.What does intrinsic factor do?
  5. Q5.Name the enzymes digesting proteins.
  6. Q6.List four functions of the liver.

Long-answer questions

  1. Q1.Describe body fluid compartments and electrolyte balance.
  2. Q2.Describe the structure and functions of the digestive organs.
  3. Q3.Describe the digestion of carbohydrates, proteins and lipids.
  4. Q4.Describe the structure and functions of the liver.

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