Speaking from experience....TBI doesn't have to just be a severe physical blow as it could happen in other ways (such as severe electrocution).
Also, it depends on how hard the injury was to the hippocampus, which then starts affects pituatary gland, and then the rest of the body.
Next, don't just think about it in terms of anatomy. Rats and humans have different levels of memory, consciousness and also life spans. Since a human lives longer, they're likely to receive more than just TBI. I've had ....more than a lion's share.

Effects do COMPOUND, which will affect the nervous sytem & endocrine system as well (which will affect the rest of the body as well). It also has a more psychological effect on humans, since it can result in low confidence, poor self image, which can cause slouching & the posture (due to bending of spine) will start releasing more cortisol. This creates a sympathetic response (fight/flight/freeze/fawn/faint), during which the hyptothalamus sends signals to various parts:
Your sympathetic nervous system controls your “fight-or-flight” response. Danger or stress activates your sympathetic nervous system, which can cause several things to happen in your body. In response to danger or stress, your sympathetic nervous system may affect your:
"Eyes. Enlarge your pupils to let more light in and improve your vision.
Heart. Increase your heart rate to improve the delivery of oxygen to other parts of your body.
Lungs. Relax your airway muscles to improve oxygen delivery to your lungs.
Digestive tract. Slow down your digestion so its energy is diverted to other areas of your body.
Liver. Activate energy stores in your liver to an energy that can be used quickly.

These effects help you in situations where you might need to think or act quickly. They improve your eyesight, reflexes, endurance and strength. Your sympathetic nervous system also activates at times when your body’s under strain, like when you’re exercising or are sick.

Your sympathetic nervous system activity also affects your immune system and your body’s repair processes. These effects can help your body start repairs on an injury quickly if you get hurt." - MyClevelandClinic

Through repeated instances of TBI, one becomes more and more sensitive to acute stress to where cortisol is constantly being released & the brain is always in a hyperaware state. Now think about the effects mentioned above to the various organs when it comes to extended periods of activation of sympathetic response (which is what happens when people become more and more sensitive to stressors that it'll activate at the drop of a hat). Eyes start to get weaker, heart = hypertension, slowed digestive tract for = obesity, etc.

These symptoms are often common in various illnesses such as diabetes, so it becomes hard to understand how TBI has had an effect on causing this. Also, there is Cushings Syndome (often underdiagnosed or just misdiagnosed as just Diabetes without seeing if other symptoms exist that might require further testing & digging deeper).

To repeatedly cause TBI to humans or rats for the sake of study would be unethical. This research needs people who have already suffered multiple instances of TBI. I'm one of them & would like to see if I can help in any way.

Source:
- my.clevelandclinic.org/.../23262-sympathetic-nervous-system-sns-fight-or-flight
- Personal experience