Unit 4: Lymphatic system and sense organs
Human Anatomy and Physiology-I notes · PTU syllabus (BMLS203-18)
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Unit summary
The lymphatic system returns fluid and fights infection, and the sense organs connect us with the world. This unit covers the structure and functions of lymph nodes, spleen, thymus and tonsils, and of the eye, ear, nose and tongue.
After this unit you can
- Describe the lymphatic system and lymph nodes
- Describe the spleen, thymus and tonsils
- Describe the structure and functions of the eye and ear
- Describe the senses of smell and taste
PTU syllabus topics
- Structure and function of lymph nodes
- spleen
- thymus gland and tonsils
- structure and function of the eye
- ear
- nose and tongue
Lymph nodes
Filter lymph, house lymphocytes
Spleen
Filters blood, removes old RBCs
Thymus
T-cell maturation
Tonsils
First defence in the throat
Topic 1
The lymphatic system and lymph nodes
- Lymph: tissue fluid collected by lymphatic capillaries, flowing through lymph vessels and nodes to the thoracic duct and right lymphatic duct into the subclavian veins.
- Fluid return
- Returns excess tissue fluid and proteins to blood
- Fat absorption
- Lacteals absorb fats (chyle)
- Defence
- Lymphocytes and macrophages filter pathogens
- Lymph nodes: bean-shaped, with a capsule, cortex (follicles of B cells), paracortex (T cells) and medulla; afferent vessels enter and an efferent vessel leaves at the hilum. Groups: cervical, axillary, inguinal. Enlarged nodes suggest infection or cancer.
Topic 2
Spleen, thymus and tonsils
Spleen
Largest lymphoid organ, left upper abdomen; red pulp and white pulp
Removes old red cells and platelets; immune responses; stores platelets; blood formation in the fetus
Thymus
Two lobes behind the sternum; large in children, shrinks in adults
Maturation of T lymphocytes; thymosin hormone
Tonsils
Palatine, pharyngeal (adenoids) and lingual
First defence against inhaled and swallowed pathogens
- Primary lymphoid organs: bone marrow and thymus; secondary: lymph nodes, spleen, tonsils and mucosa-associated lymphoid tissue.
Topic 3
The eye
- Sclera and cornea
- Tough white coat; transparent front that refracts light
- Choroid, ciliary body, iris
- Vascular layer; ciliary muscles change lens shape; iris controls the pupil
- Lens
- Focuses light (accommodation)
- Retina
- Rods (dim light) and cones (colour); fovea for sharp vision; optic disc (blind spot)
- Humours
- Aqueous (front) and vitreous (back)
- Optic nerve
- Carries signals to the brain
- Defects: myopia (concave lens), hypermetropia (convex lens), cataract, glaucoma (raised intraocular pressure).
Topic 4
The ear
External ear
Pinna and auditory canal
Collects sound
Middle ear
Tympanic membrane; ossicles — malleus, incus, stapes; Eustachian tube
Amplifies and transmits vibrations; equalises pressure
Inner ear
Cochlea with organ of Corti; vestibule and semicircular canals
Hearing; balance and equilibrium
Topic 5
The nose and tongue
- Smell (olfaction): olfactory receptors in the roof of the nasal cavity detect dissolved odour molecules; signals go through the olfactory nerve to the brain.
- Taste (gustation): taste buds on tongue papillae detect sweet, salty, sour, bitter and umami; carried by facial and glossopharyngeal nerves. Smell strongly influences flavour.
Key terms
- Lymph
- Fluid flowing in lymphatic vessels
- Thymus
- Organ where T lymphocytes mature
- Retina
- Light-sensitive inner layer of the eye
- Organ of Corti
- Receptor organ of hearing
- Taste bud
- Receptor for taste
Quick revision
- Lymph flow; functions; lymph node structure and groups.
- Spleen, thymus, tonsils; primary and secondary lymphoid organs.
- Eye layers, lens, retina, rods and cones; refractive errors.
- External, middle, inner ear; hearing and balance.
- Olfaction; taste buds and five tastes.
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
- Q1.Give two functions of the lymphatic system.
- Q2.Name the primary lymphoid organs.
- Q3.What is the function of the spleen?
- Q4.Distinguish rods and cones.
- Q5.Name the ear ossicles.
- Q6.What is umami?
Long-answer questions
- Q1.Describe the lymphatic system and the structure of a lymph node.
- Q2.Describe the spleen, thymus and tonsils.
- Q3.Describe the structure and functions of the eye.
- Q4.Describe the structure of the ear and the mechanisms of hearing and balance.
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