Urination

 Are the muscles on the sphincters continuously activated (to keep them closed)?

What is the pressure built inside the bladder?

Urinary Catheter

Description. Some highlights:

• Size: (bore) diameter 6 to 18 Fr, with Fr=0.33mm. Usually 14 or 16 Fr, i.e., 4.62mm or 5.28mm.
• Balloon size: 5ml or 10ml. More than that (say 30ml) only for special applications (like putting pressure on the prostate after surgery to help it heal).

Excellent paper on the issues with indwelling urinary catheters

https://www.researchgate.net/profile/Calvin-Kunin

Urethra

Links with many details:

• Urethra anatomy
• Urothelium (urethra lining)
• Urethral Lumen Cross-section

Some highlights:

• Length (average, male): 22 cm 
• Diameter: I guess it stretches? For reference, a ureteroscope like this is about 2.8mm in diameter. A urinary catheter ranges from 4.62mm or 5.28mm
• Cross section and number of cells
• Male urethral cancers account for less than 1% of urologic malignancies
• Internal and external sphincters

Distal (furthest from the body) output orifice (the point where urine exits the urethra): Urinary meatus

Cells FAQ

How many are there in the body? ~37 Trillion (37e12) + 10-100 Trillion microbial cells in the microbiota.

How many by tissue? This nice supplemental material to this article is so far the closest I've found to answer this (thanks to these guys).

How often they divide? See same material.

How many types? According to this site, about 200. There are whole collaborations like the Human Cell Atlas trying to list these. It is not obvious how to classify what makes a cell fall on a different group than another. 

https://www.biolegend.com/en-us/cell-markers

https://en.wikipedia.org/wiki/List_of_human_cell_types_derived_from_the_germ_layers

How to distinguish them? 

• Using surface cell markers
• Beautiful resource

What makes us call a type different from another type?

At what point they are differentiated?

What is CD? Molecules expressed on the cell surface that allow for their differentiation by scientist but also by the immune system (and not necessarily in that order :)). Full list here.

Here I list few known ones:

• Stem cells:
• Embryonic
• Somatic or adult << We would count only these in an adult
• Red blood cells: erythrocytes. Fun fact: they do not have nuclei
• White blood cells (leukocytes):
• Granulocytes
• Neutrophils
• Eosinophils
• Basophils
• Agranulocytes
• Lymphocytes:
• B-cells
• T-cells
• Monocytes.
• Platelets: actually megakaryocytes 
• Nerve cells: neurons
• Neuroglial (aka glial) cells
• Astrocytes
• Oligodendrocytes
• Microglial cells
• Ependymal cells
• Schwan cells
• Satellite cells
• Muscle (aka myocytes) cells:
• Skeletal muscle cell: multinucleated, cm long, form voluntary muscles (muscles controlled by the somatic nervous system)
• Cardiac muscle cell, aka cardiomyocytes 
• Smooth muscle cell, responsible for involuntary contractions.
• Cartilage cells, aka chondrocytes
• Bone cells:
• Osteoblasts
• Osteoclasts
• Osteocytes
• Lining cells.
• Skin cells:
• Keratinocytes
• Melanocytes
• Langerhans cells
• Merkel cells: involved in touch
• Endothelial cells: blood vessel lining
• Epithelial cells: lining of cavities in the body
• Fat cells, aka adipocytes and lipocytes 
• White fat cells
• Brown fat cells
• Sex cells: sperm or ova (eggs)

(Last Update: 1/12/2023)