EXAM QUESTIONS
1. The cell is like a ‘factory’, with its own internal processes and homeostasis, as
well as having interactions with other cells and tissues. Describe how a cell does
this. Make reference to its various components, with emphasis on how they
interact with each other, and how they assist the cell in its function. Also make
reference to how the cell interacts with its environment (~18 marks, ~15 minutes).
-
Cells are dynamic basic structural and functional units of the body
E.g. protein production illustrates interaction between organelles and the
surrounding environment for an ultimately homeostatic cause
Organelle
Mitochondria
Nucleus
Function
- Produce ATP through aerobic cellular respiration (via enzymes
within inner mitochondrial membrane)
- Provides energy for homeostatic functions (e.g. protein production)
- ‘Cell powerhouse’
- Command centre
- Controls cell activity (e.g. drives protein production) through
carrying DNA (genetic material stored a condensed chromatin)
- Contains nuclear membrane (phospholipid bilayer), which
incorporates nuclear pores for mRNA movement into cytoplasm
during protein production (transcription)
Ribosome
-
ER (endoplasmic
reticulum)
-
Produce proteins (site of translation) destined for cytosolic function
Free ribosomes, OR alpha and beta structures dock onto ER
membrane
Rough endoplasmic reticulum (RER) = layers (cisternae) of
plasma membrane and embedded surface ribosomes
Proteins produced here destined for incorporation into
plasmalemma or exportation
Smooth endoplasmic reticulum (SER) = layers (cisternae) of
- Tight ‘locked together’ arrangement of concentric lamellar layers and separate osteons
provides general strength
• Ensure bone matrix incompressible
• Inner layers buck against outer layers
- Ground substances of inorganic salts (e.g. calcium) provide strength under
compression = ‘concrete’ = can’t be push together
- Collagen (tough, non-stretch) provides strength under tension = ‘reinforcing rod’ =
can’t pull apart AND under twisting (torsion) (alternating 90 degree arrangement of
collagen fibres between adjacent lamellae means twisting one way resisted by collagen
fibres of deep concentric layer)
b) Bone gets remodelled when the stresses on it change, or as part of the body’s
mineral homeostasis. Discuss how this happens and illustrate your answer with
an example.
Bone remodelling due to stress change:
- Stressing bone generates peso-electric current
- Loading bone ‘bulks up’ area (osteoblasts)
- De-loading bone resorbs bone in specific non-essential area (osteoclasts)
- E.g. fractured bone: Haemotoma > fibrocartilagenous callus > bony callus
formation > excessive bone remodelled and refined to suit stress. Due to
increased osteoblastic action (initially) to lay down bone and increased
osteoclastic action (finally) to smooth excess (spongy) bone. Involves
remodelling process.
Bone remodelling due to mineral homeostasis:
- Bone contributes to controlling mineral homeostasis by acting as a mineral
reservoir (storing calcium)
- Calcium necessary for neural and muscle function released into bloodstream
through the resorbing action of osteoclasts as needed (e.g. via decreased blood
calcium levels triggering PTH from parathyroid glands), or deposited within bone
through the calcifying action of osteoblasts when needed (e.g. via increased
blood calcium levels triggering calcitonin release from thyroid gland).
= remodelling process which restores blood calcium balance
- I. e. Balance of calcium maintained through balancing osteoblast and osteoclast
action through hormonal control
- E.g. Osteoporosis:
• Less calcification (via action of calcitonin triggering osteoblasts) into bone
during later life (more osteoclast function via PTH trigger necessary to
attempt restoration of low blood calcium levels)
• Net calcium loss in bone causes osteoporosis (bone weakness and
brittleness)
Osteoblast
- Mitochondria
- Calcify matrix
Osteoclast
- Many nuclei
- Resorb and recycle (releases
3. a) Describe the structure of the three main types of joints in the body, and give
an example of each. Broadly describe what types of movement can occur around
each those joints, and why they are constructed the way they are.
Joints – link bones and are stabilised, aided or restricted by ligaments / tendons
Fibrous joint
-
Cartilaginous joint
-
Synovial joint
-
-
Bones bound by inflexible fibrous connective tissue fibres
No (completely restricted) appreciable movement at
involved bones
Less mobile
No flexibility
Found in non-locomotive areas
Allow for minimal movement between plates and provide
resilience
E.g. skull (cranial) bones
• Inter-digitating suture joints
• Very strong
• Via dense fibrous connective tissue fibres
• Ossify (fuse) over time
Bones linked by cartilage
Some movement either side of joint
Somewhat mobile
Some flexibility
E.g. sychondroses = ribs attach to sternum via slightly
elastic and strong hyaline costal cartilage which permits
rib movement during respiration
Bones linked by fluid-filled joint cavity
Protective and strong
Lubricates bone surface on either side of joint
Most common
Maximum mobility and flexibility
Consists of:
1. Articular cartilage lining covering outer bone
2. Articular capsule surrounding joint = fibrous capsule +
synovial membrane
3. Synovial fluid (protection, lubrication, nutrition,
prevents friction) filling articular capsule and produced
within capsule
4. Joint (synovial) cavity
5. Articular discs within joint subject to more wear and
tear
6. Tendons and ligaments surrounding joint to provide
stability and permit or constrain movement at joint
Enables either non-axial, uni-axial, bi-axial, or tri-axial
movement around joint (i.e. differing flexibility and axis of
movement)